Faculty Profiles - HISHIKAWA, Akiyoshi

Papers - HISHIKAWA, Akiyoshi

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Wave-packet manipulation of He Rydberg states by a seeded free-electron laser Reviewed International coauthorship

Mathieu Dumergue, Paolo Antonio Carpeggiani, Tamás Csizmadia, Miltcho Danailov, Alexander Demidovich, Giovanni De Ninno, Michele Di Fraia, Per Eng-Johnsson, Dominik Ertel, Hikaru Fujise, Mizuho Fushitani, Luca Giannessi, Harshitha Nandiga Gopalakrishna, Akiyoshi Hishikawa, Heide Ibrahim, Sergei Kühn, Francois Légaré, Yu Luo, Praveen Kumar Maroju, Johan Mauritsson, Matteo Moioli, Anna Olofsson, Jasper Peschel, Oksana Plekan, Stephen T. Pratt, Lorenzo Raimondi, Primož Rebernik Ribič, Shu Saito, Giuseppe Sansone, Ronak Shah, Emma R. Simpson, Daehyun You, Marco Zangrando, Carlo Callegari, Kiyoshi Ueda, Kevin C. Prince

Physical Review Research Vol. 6 ( 4 ) 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society (APS)

We report a two-dimensional pump-control-probe spectroscopic study of the dynamics of singly excited He Rydberg-state wave packets with a seeded extreme ultraviolet (XUV) free-electron laser (FEL) source. A pair of coherent XUV pulses, defined by their coarse time separation and relative phase, created and manipulated the wave packets. The He atoms were postionized by infrared (IR) pulses, and the ion yield was measured as a function of XUV phase and IR arrival time. We tagged and sorted the relative phase of the XUV pulse pair on a single-shot basis by fitting each FEL spectrum with a suitable function that accounts for nonidealities of the XUV pulse pairs, associated with the seeding process; more generally, the fit returns the time-dependent electric field of the FEL spectra. The experimental two-dimensional maps of ion yields, measured as a function of IR (probe) delay and of XUV (pump-control) phase, were compared with the solution of the first-order time-dependent Schrödinger equation for this field. Despite the fact that the experimental conditions imply strong excitation, beyond the approximations of first-order perturbation theory, the simulated map satisfactorily reproduces the experimental one for temporally well-separated pulses. We show that by selecting data at appropriate values of pump-control phase, we enhance or suppress the amplitude of chosen wave-packet components consisting of two or more Rydberg states. When the temporal overlap of the pulse pair cannot be neglected, the phase reconstruction is underdetermined, and we provide a simplified comparison between data and simulations.

Published by the American Physical Society 2024

DOI： 10.1103/PhysRevResearch.6.043323

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.6.043323/fulltext

Ion-core switching in Rydberg series of XeKr Reviewed

Fukuda, Y., Szidarovszky, T., Nakata, M., Hishikawa, A., Yamanouchi, K.

Molecular Physics Vol. 122 ( 15-16 ) 2024.8

State-selective dissociative double ionization of CH3I and CH2I2 via I 4d core-hole states studied by multi-electron–ion coincidence spectroscopy Reviewed

Mizuho Fushitani, Yasumasa Hikosaka, Motomichi Tashiro, Akiyoshi Hishikawa

The Journal of Chemical Physics Vol. 160 ( 17 ) 2024.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Publishing

The dissociative double ionization of CH3I and CH2I2 irradiated with extreme ultraviolet light at hv = 100 eV is investigated by multi-electron–ion coincidence spectroscopy using a magnetic bottle type electron spectrometer. The spin–orbit state-resolved Auger electron spectra for the I 4d core-hole states, (I 4d3/2)−1 and (I 4d5/2)−1, provide clear identifications of electronic states of CH3I2+ and CH2I22+. The dominant ion species produced after the double ionization correlate with the Auger electron energy, showing that different fragmentation pathways are open depending on the electronic states populated by the Auger decay. Theoretical calculations are performed to understand the fragmentation from the doubly charged states and the observed spin–orbit specificity in the Auger decay.

DOI： 10.1063/5.0204769

Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes <i>via</i> site-selective ionization Reviewed Open Access

Weronika O. Razmus, Felix Allum, James Harries, Yoshiaki Kumagai, Kiyonobu Nagaya, Surjendu Bhattacharyya, Mathew Britton, Mark Brouard, Philip H. Bucksbaum, Kieran Cheung, Stuart W. Crane, Mizuho Fushitani, Ian Gabalski, Tatsuo Gejo, Aaron Ghrist, David Heathcote, Yasumasa Hikosaka, Akiyoshi Hishikawa, Paul Hockett, Ellen Jones, Edwin Kukk, Hiroshi Iwayama, Huynh V. S. Lam, Joseph W. McManus, Dennis Milesevic, Jochen Mikosch, Shinichirou Minemoto, Akinobu Niozu, Andrew J. Orr-Ewing, Shigeki Owada, Daniel Rolles, Artem Rudenko, Dave Townsend, Kiyoshi Ueda, James Unwin, Claire Vallance, Anbu Venkatachalam, Shin-ichi Wada, Tiffany Walmsley, Emily M. Warne, Joanne L. Woodhouse, Michael Burt, Michael N. R. Ashfold, Russell S. Minns, Ruaridh Forbes

Physical Chemistry Chemical Physics Vol. 26 ( 16 ) page： 12725 - 12737 2024.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

The dissociation dynamics of UV pumped iodothiophene molecules are investigated using velocity map ion imaging, in combination with site-selective extreme ultraviolet ionization of the iodine atom.

DOI： 10.1039/d3cp06079a

Wave packet dynamics and control in excited states of molecular nitrogen Reviewed International coauthorship

Mizuho Fushitani, Hikaru Fujise, Akiyoshi Hishikawa, Daehyun You, Shu Saito, Yu Luo, Kiyoshi Ueda, Heide Ibrahim, Francois Légaré, Stephen T. Pratt, Per Eng-Johnsson, Johan Mauritsson, Anna Olofsson, Jasper Peschel, Emma R. Simpson, Paolo Antonio Carpeggiani, Dominik Ertel, Praveen Kumar Maroju, Matteo Moioli, Giuseppe Sansone, Ronak Shah, Tamás Csizmadia, Mathieu Dumergue, Harshitha Nandiga Gopalakrishna, Sergei Kühn, Carlo Callegari, Miltcho Danailov, Alexander Demidovich, Lorenzo Raimondi, Marco Zangrando, Giovanni De Ninno, Michele Di Fraia, Luca Giannessi, Oksana Plekan, Primoz Rebernik Ribic, Kevin C. Prince

The Journal of Chemical Physics Vol. 160 ( 10 ) 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Publishing

Wave packet interferometry with vacuum ultraviolet light has been used to probe a complex region of the electronic spectrum of molecular nitrogen, N2. Wave packets of Rydberg and valence states were excited by using double pulses of vacuum ultraviolet (VUV), free-electron-laser (FEL) light. These wave packets were composed of contributions from multiple electronic states with a moderate principal quantum number (n ∼ 4–9) and a range of vibrational and rotational quantum numbers. The phase relationship of the two FEL pulses varied in time, but as demonstrated previously, a shot-by-shot analysis allows the spectra to be sorted according to the phase between the two pulses. The wave packets were probed by angle-resolved photoionization using an infrared pulse with a variable delay after the pair of excitation pulses. The photoelectron branching fractions and angular distributions display oscillations that depend on both the time delays and the relative phases of the VUV pulses. The combination of frequency, time delay, and phase selection provides significant control over the ionization process and ultimately improves the ability to analyze and assign complex molecular spectra.

DOI： 10.1063/5.0188182

Imaging Ultrafast Dissociation Dynamics: OCS & Roaming in Formaldehyde International coauthorship Open Access

Endo, T; Neville, SP; Ziems, KM; Lassonde, P; Qu, C; Schmidt, BE; Fujise, H; Fushitani, M; Hishikawa, A; Grafe, S; Houston, PL; Bowman, JM; Schuurman, MS; Legare, F; Ibrahim, H

PROCEEDINGS OF THE 8TH INTERNATIONAL CONFERENCE ON ATTOSECOND SCIENCE AND TECHNOLOGY, ATTO 2023 Vol. 300 page： 75 - 82 2024

Publisher：Springer Proceedings in Physics

Upon photoexcitation, molecules break apart, following different dissociation reactions. We can image these dissociation pathways using Coulomb explosion imaging (CEI) and sometimes we can control them using asymmetric laser fields. In the formaldehyde molecule, we can see fragments following the direct, conventional dissociation path, as well as fragments deviating from this minimum energy path. So-called roaming fragments or “roamers” explore the potential energy landscape in a statistical manner and could be directly captured in real-time, despite the signal’s statistical character. This is possible due to the single-molecule sensitivity of CEI and we could show that the onset of roaming occurs actually several orders of magnitude earlier than previously expected. In the polar molecule OCS we go one step further by controlling the fragmentation process using two-color asymmetric laser fields. In addition to expected direct ionization effects, we also see post-ionization contributions, which are usually not visible in heavy polar molecules. We thus show in two different examples that CEI provides the means to extract new, unexpected pathways, which would otherwise remain hidden underneath a strong background.

DOI： 10.1007/978-3-031-47938-0_8

Dissociative ionization and Coulomb explosion of CH<sub>4</sub> in two-color asymmetric intense laser fields Reviewed International coauthorship

H. Hasegawa, A. Matsuda, T. Morishita, L. B. Madsen, F. Jensen, O. I. Tolstikhin, A. Hishikawa

Physical Chemistry Chemical Physics Vol. 25 ( 37 ) page： 25408 - 25419 2023.9

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

Three-dimensional ion momentum imaging reveals that methane in two-color asymmetric intense laser fields has different waveform dependence for atomic and molecular hydrogen ion ejection.

DOI： 10.1039/d3cp02337k

Capturing transient core-to-core resonances in Kr in intense extreme-ultraviolet laser fields by electron-ion coincidence spectroscopy Reviewed

Mizuho Fushitani, Makoto Yamada, Hikaru Fujise, Shigeki Owada, Tadashi Togashi, Kyo Nakajima, Makina Yabashi, Akitaka Matsuda, Yasumasa Hikosaka, Akiyoshi Hishikawa

Physical Review A Vol. 107 ( 2 ) page： L021101 2023.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society (APS)

DOI： 10.1103/PhysRevA.107.L021101

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevA.107.L021101/fulltext

Orbital effects on tunnel-electron momentum distributions: Ar and H2 studied by electron–ion coincidence momentum imaging Reviewed Open Access

Daimu Ikeya, Hikaru Fujise, Shinnosuke Inaba, Minami Takahashi, Masateru Yamamoto, Takeru Nakamura, Yu Nagao, Akitaka Matsuda, Mizuho Fushitani, Akiyoshi Hishikawa

Journal of Electron Spectroscopy and Related Phenomena Vol. 262 page： 147280 - 147280 2023.1

Imaging and Controlling ultrafast Dissociation Dynamics; from conventional to surprising paths

Endo T., Neville S.P., Lassonde P., Qu C., Schmidt B.E., Fushitani M., Hishikawa A., Houston P.L., Bowman J.M., Schuurman M.S., Légaré F., Ibrahim H.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 12419 2023

Publisher：Proceedings of SPIE - The International Society for Optical Engineering

Upon photo-excitation of a molecule it will break apart. We can see fragments following direct, conventional dissociation paths, as well as fragments deviating from this minimum energy path. The latter are called roaming fragments and explore the potential energy landscape in a statistical manner. Dissociating and roaming fragments are directly captured using Coulomb explosion imaging (CEI) and individual pathways are distinguished based on state-of-the-art theory analysis.

DOI： 10.1117/12.2649247

Following ultrafast Roaming Dissociation Dynamics with Coulomb Explosion Imaging

Endo T., Neville S., Lassonde P., Qu C., Fujise H., Fushitani M., Hishikawa A., Houston P., Bowman J., Légaré F., Schuurman M., Ibrahim H.

2023 Conference on Lasers and Electro-Optics, CLEO 2023 2023

Following ultrafast Roaming Dissociation Dynamics with Coulomb Explosion Imaging

Endo T., Neville S., Lassonde P., Qu C., Fujise H., Fushitani M., Hishikawa A., Houston P., Bowman J., Légaré F., Schuurman M., Ibrahim H.

CLEO: Fundamental Science, CLEO:FS 2023 2023

Asymmetric Dissociative Tunneling Ionization of Tetrafluoromethane in ω − 2ω Intense Laser Fields Invited Reviewed Open Access

Hiroka Hasegawa, Tiffany Walmsley, Akitaka Matsuda, Toru Morishita, Lars Bojer Madsen, Frank Jensen, Oleg I. Tolstikhin, Akiyoshi Hishikawa

Frontiers in Chemistry Vol. 10 2022.4

Authorship：Last author,　Corresponding author Publishing type：Research paper (scientific journal) Publisher：Frontiers Media {SA}

<jats:p>Dissociative ionization of tetrafluoromethane (CF<jats:sub>4</jats:sub>) in linearly polarized <jats:italic>ω</jats:italic>-2<jats:italic>ω</jats:italic> ultrashort intense laser fields (1.4 × 10<jats:sup>14</jats:sup> W/cm<jats:sup>2</jats:sup>, 800 and 400 nm) has been investigated by three-dimensional momentum ion imaging. The spatial distribution of <jats:inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m1"><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></jats:inline-formula> produced by CF<jats:sub>4</jats:sub> → <jats:inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m2"><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></jats:inline-formula> + F + e<jats:sup>−</jats:sup> exhibited a clear asymmetry with respect to the laser polarization direction. The degree of the asymmetry varies by the relative phase of the <jats:italic>ω</jats:italic> and 2<jats:italic>ω</jats:italic> laser fields, showing that 1) the breaking of the four equivalent C-F bonds can be manipulated by the laser pulse shape and 2) the C-F bond directed along the larger amplitude side of the <jats:italic>ω</jats:italic>-2<jats:italic>ω</jats:italic> electric fields tends to be broken. Weak-field asymptotic theory (WFAT) shows that the tunneling ionization from the 4<jats:italic>t</jats:italic><jats:sub>2</jats:sub> second highest-occupied molecular orbital (HOMO-1) surpasses that from the 1<jats:italic>t</jats:italic><jats:sub>1</jats:sub> HOMO. This predicts the enhancement of the tunneling ionization with electric fields pointing from F to C, in the direction opposite to that observed for the asymmetric fragment ejection. Possible mechanisms involved in the asymmetric dissociative ionization, such as post-ionization interactions, are discussed.</jats:p>

DOI： 10.3389/fchem.2022.857863

Helicity-dependent dissociative tunneling ionization of CF4 in multicycle circularly polarized intense laser fields Reviewed

H. Fujise, M. Uemura, H. Hasegawa, D. Ikeya, A. Matsuda, T. Morishita, L. B. Madsen, F. Jensen, O. I. Tolstikhin, A. Hishikawa

Physical Chemistry Chemical Physics Vol. 24 ( 15 ) page： 8962 - 8969 2022.4

Authorship：Last author,　Corresponding author Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry ({RSC})

Three-dimensional electron–ion coincidence momentum imaging reveals that the dissociative tunneling ionization of tetrafluoromethane (CF<sub>4</sub>) is sensitive to the helicity of the circularly polarized laser fields.

DOI： 10.1039/d1cp05858d

Post-Ionization Dynamics of the Polar Molecule OCS in Asymmetric Laser Fields Invited Reviewed International coauthorship Open Access

Tomoyuki Endo, Karl Michael Ziems, Martin Richter, Friedrich G. Fröbel, Akiyoshi Hishikawa, Stefanie Gräfe, Fran{\c{c } }ois, L{\'{e } }gar{\'{e, Heide Ibrahim

Frontiers in Chemistry Vol. 10 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers Media {SA}

<jats:p>We have investigated the dissociation mechanisms of the prototypical heavy polar molecule OCS into the two break-up channels of the dication, OCS<jats:sup>2+</jats:sup> → O<jats:sup>+</jats:sup> + CS<jats:sup>+</jats:sup> and OC<jats:sup>+</jats:sup> + S<jats:sup>+</jats:sup>, in phase-locked two-color intense laser fields. The branching ratio of the breaking of the C–O and C–S bonds followed a pronounced 2<jats:italic>π</jats:italic>-oscillation with a modulation depth of 11%, depending on the relative phase of the two-color laser fields. The fragment ejection direction of both break-up channels reflects the anisotropy of the tunneling ionization rate, following a 2<jats:italic>π</jats:italic>-periodicity, as well. The two dissociation pathways in the C–S bond breaking channel show different phase dependencies of the fragment ejection direction, which are assigned to post-ionization dynamics. These observations, resulting from the excitation with asymmetric two-color intense laser fields, supported by state-of-the-art theoretical simulations, reveal the importance of post-ionization population dynamics in addition to tunneling ionization in the molecular fragmentation processes, even for heavy polar molecules.</jats:p>

DOI： 10.3389/fchem.2022.859750

Electronic relaxation and dissociation dynamics in formaldehyde: pump wavelength dependence Reviewed Open Access

Tomoyuki Endo, Simon P. Neville, Philippe Lassonde, Chen Qu, Hikaru Fujise, Mizuho Fushitani, Akiyoshi Hishikawa, Paul L. Houston, Joel M. Bowman, François Légaré, Michael S. Schuurman, Heide Ibrahim

Physical Chemistry Chemical Physics Vol. 24 ( 3 ) page： 1779 - 1786 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry ({RSC})

The effect of the incident UV pump wavelength on the subsequent excited state dynamics, elec- tronic relaxation, and ultimate dissociation of formaldehyde is studied using ﬁrst principles simu- lation and...

DOI： 10.1039/d1cp04264e

Electron-ion Coincidence Imaging of O<inf>2</inf> in Intense Laser Fields with Additional Dissociation Pulses

Ikeya D., Matsuda A., Fushitani M., Hishikawa A.

Optics InfoBase Conference Papers 2022

Selective-bond breaking of CF<inf>4</inf> in phase-locked ω-2ω intense laser fields

Hasegawa H., Walmsley T., Matsuda A., Morishita T., Madsen L.B., Jensen F., Tolstikhin O.I., Hishikawa A.

Optics InfoBase Conference Papers 2022

Roaming in Formaldehyde – and how to get there

Endo T., Neville S.P., Lassonde P., Qu C., Fujise H., Fushitani M., Hishikawa A., Houston P.L., Bowman J.M., Légaré F., Schuurman M.S., Ibrahim H.

Optics InfoBase Conference Papers 2022

Post-Ionization Interaction of OCS in Phase-Locked Two-Color Laser Fields

Endo T., Ziems K.M., Richter M., Froebel F.G., Hishikawa A., Gräfe S., Légaré F., Ibrahim H.

Optics InfoBase Conference Papers 2022

Selective-bond breaking of CF4 in phase-locked ω-2ω intense laser fields

Hiroka Hasegawa, Tiffany Walmsley, Akitaka Matsuda, Toru Morishita, Lars Bojer Madsen, Frank Jensen, Oleg I. Tolstikhin, Akiyoshi Hishikawa

The International Conference on Ultrafast Phenomena (UP) 2022 2022

Association Reaction of Gaseous C2H4 in Femtosecond Laser Filaments Studied by Time-of-Flight Mass Spectrometry Reviewed Open Access

Akitaka Matsuda, Kentaro Tani, Yukari Takeuchi, Yui Hayakawa, Akiyoshi Hishikawa

ACS Omega Vol. 6 ( 44 ) page： 29862 - 29868 2021.11

Time-resolved shot-by-shot photoelectron spectroscopy of autoionizing Xe+ states by EUV–free-electron-laser and near-IR laser pulses Reviewed

Akiyoshi Hishikawa

Physical Review A Vol. 104 ( 2 ) 2021.8

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society (APS)

DOI： 10.1103/PhysRevA.104.023102

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevA.104.023102/fulltext

Time-resolved photoelectron imaging of complex resonances in molecular nitrogen Reviewed International coauthorship Open Access

Mizuho Fushitani, Stephen T. Pratt, Daehyun You, Shu Saito, Yu Luo, Kiyoshi Ueda, Hikaru Fujise, Akiyoshi Hishikawa, Heide Ibrahim, François Légaré, Per Johnsson, Jasper Peschel, Emma R. Simpson, Anna Olofsson, Johan Mauritsson, Paolo Antonio Carpeggiani, Praveen Kumar Maroju, Matteo Moioli, Dominik Ertel, Ronak Shah, Giuseppe Sansone, Tamás Csizmadia, Mathieu Dumergue, N. G. Harshitha, Sergei Kühn, Carlo Callegari, Oksana Plekan, Michele Di Fraia, Miltcho B. Danailov, Alexander Demidovich, Luca Giannessi, Lorenzo Raimondi, Marco Zangrando, Giovanni De Ninno, Primož Rebernik Ribič, Kevin C. Prince

The Journal of Chemical Physics Vol. 154 ( 14 ) page： 144305 - 144305 2021.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AIP Publishing

We have used the FERMI free-electron laser to perform time-resolved photoelectron imaging experiments on a complex group of resonances near 15.38 eV in the absorption spectrum of molecular nitrogen, N , under jet-cooled conditions. The new data complement and extend the earlier work of Fushitani et al. [Opt. Express 27, 19702-19711 (2019)], who recorded time-resolved photoelectron spectra for this same group of resonances. Time-dependent oscillations are observed in both the photoelectron yields and the photoelectron angular distributions, providing insight into the interactions among the resonant intermediate states. In addition, for most states, we observe an exponential decay of the photoelectron yield that depends on the ionic final state. This observation can be rationalized by the different lifetimes for the intermediate states contributing to a particular ionization channel. Although there are nine resonances within the group, we show that by detecting individual photoelectron final states and their angular dependence, we can identify and differentiate quantum pathways within this complex system. 2

DOI： 10.1063/5.0046577

Other Link： https://aip.scitation.org/doi/pdf/10.1063/5.0046577

On the measurement of statistical dynamics using the method of Coulomb explosion imaging

Tomoyuki Endo, Simon P. Neville, Vincent Wanie, Samuel Beaulieu, Chen Qu, Philippe Lassonde, Bruno E. Schmidt, Hikaru Fujise, Mizuho Fushitani, Akiyoshi Hishikawa, Paul L. Houston, Joel M. Bowman, Michael S. Schuurman, François Légaré, Heide Ibrahim

AIP Conference Proceedings Vol. 2343 2021.3

Language：Japanese Publishing type：Research paper (international conference proceedings)

Using time-resolved Coulomb explosion imaging (CEI) in an ultraviolet (UV) pump near infrared (NIR) probe experiment, we directly image the different dissociation dynamics in the formaldehyde molecule. Different pathways are distinguished from each other, despite their statistical nature. To extract such dynamics, hidden in a statistical background, calls for an elimination of noise. In our approach, we take advantage of CEI being a quasi-background-free technique.

DOI： 10.1063/5.0047930

Capturing roaming molecular fragments in real time Reviewed International coauthorship International journal

Tomoyuki Endo, Simon P. Neville, Vincent Wanie, Samuel Beaulieu, Chen Qu, Jude Deschamps, Philippe Lassonde, Bruno E. Schmidt, Hikaru Fujise, Mizuho Fushitani, Akiyoshi Hishikawa, Paul L. Houston, Joel M. Bowman, Michael S. Schuurman, François Lé garé, Heide Ibrahim

Science Vol. 370 ( 6520 ) page： 1072 - + 2020.11

Language：English Publishing type：Research paper (scientific journal) Publisher：American Association for the Advancement of Science ({AAAS})

<jats:p>Since the discovery of roaming as an alternative molecular dissociation pathway in formaldehyde (H<jats:sub>2</jats:sub>CO), it has been indirectly observed in numerous molecules. The phenomenon describes a frustrated dissociation with fragments roaming at relatively large interatomic distances rather than following conventional transition-state dissociation; incipient radicals from the parent molecule self-react to form molecular products. Roaming has been identified spectroscopically through static product channel–resolved measurements, but not in real-time observations of the roaming fragment itself. Using time-resolved Coulomb explosion imaging (CEI), we directly imaged individual “roamers” on ultrafast time scales in the prototypical formaldehyde dissociation reaction. Using high-level first-principles simulations of all critical experimental steps, distinctive roaming signatures were identified. These were rendered observable by extracting rare stochastic events out of an overwhelming background using the highly sensitive CEI method.</jats:p>

DOI： 10.1126/science.abc2960

Capturing roaming fragments in real time: A molecular road movie

Endo T., Neville S.P., Wanie V., Beaulieu S., Qu C., Deschamps J., Lassonde P., Schmidt B.E., Fujise H., Fushitani M., Hishikawa A., Houston P.L., Bowman J.M., Schuurman M.S., Légaré F., Ibrahim H.

Optics InfoBase Conference Papers 2020.11

Ultrafast Reaction Imaging and Control by Ultrashort Intense Laser Pulses Invited Reviewed Open Access

Akiyoshi Hishikawa, Akitaka Matsuda, Mizuho Fushitani

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 93 ( 11 ) page： 1293 - 1304 2020.11

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

Molecules irradiated with intense laser pulses (field intensity similar to 10(15) W/cm(2)) exhibit a variety of characteristic processes, such as tunneling ionization, electron rescattering, high-order harmonics generation and Coulomb explosion, that cannot be seen in a weak light field. These features have attracted attention in the last decades as they provide unique approaches to visualize and manipulate ultrafast dynamics of atoms and molecules. Here we discuss molecular processes in intense laser fields, with focuses on the applications to ultrafast imaging and control of reaction dynamics.

DOI： 10.1246/bcsj.20200158

Characterization of soft X-ray FEL pulse duration with two-color photoelectron spectroscopy Reviewed

Shigeki Owada, Mizuho Fushitani, Akitaka Matsuda, Hikaru Fujise, Yuuma Sasaki, Yasumasa Hikosaka, Akiyoshi Hishikawa, Makina Yabashi

JOURNAL OF SYNCHROTRON RADIATION Vol. 27 ( 5 ) page： 1362 - 1365 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：INT UNION CRYSTALLOGRAPHY

The pulse duration of soft X-ray free-electron laser (FEL) pulses of SACLA BL1 (0.2-0.3 nC per bunch, 0.5-0.8 MeV) were characterized by photoelectron sideband measurements. The intensity of the He 1 s(-1) photoelectron sidebands generated by a near-infrared femtosecond laser was measured as a function of the time delay between the two pulses using an arrival time monitor. From the width of the cross-correlation trace thus derived, the FEL pulse duration was evaluated to be 28 +/- 5 fs full width at half-maximum in the photon energy range between 40 eV and 120 eV.

DOI： 10.1107/S1600577520008516

Multielectron-Ion Coincidence Spectroscopy of Xe in Extreme Ultraviolet Laser Fields: Nonlinear Multiple Ionization via Double Core-Hole States Reviewed International journal

M. Fushitani, Y. Sasaki, A. Matsuda, H. Fujise, Y. Kawabe, K. Hashigaya, S. Owada, T. Togashi, K. Nakajima, M. Yabashi, Y. Hikosaka, A. Hishikawa

Physical Review Letters Vol. 124 ( 19 ) 2020.5

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society ({APS})

DOI： 10.1103/PhysRevLett.124.193201

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.124.193201/fulltext

Angle dependence of dissociative tunneling ionization of NO in asymmetric two-color intense laser fields Reviewed

Tomoyuki Endo, Hikaru Fujise, Hiroka Hasegawa, Akitaka Matsuda, Mizuho Fushitani, Oleg I. Tolstikhin, Toru Morishita, Akiyoshi Hishikawa

Physical Review A Vol. 100 ( 5 ) page： 053422 2019.11

Authorship：Last author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal)

© 2019 American Physical Society. Dissociative tunneling ionization of nitric oxide (NO) in linearly polarized phase-locked two-color femtosecond intense laser fields (45 fs, λ=800 and 400 nm, total field intensity I=1×1014W/cm2) has been studied by three-dimensional ion momentum imaging. The N+ fragment produced by the dissociative ionization, NO→NO++e-→N++O+e-, exhibits a butterflylike momentum distribution peaked at finite angles with respect to the laser polarization direction. In addition, a clear dependence on the relative phase between the two laser fields is observed, showing that the tunneling ionization occurs efficiently when the electric field points from N to O. For the highest kinetic energy component, the observed orientation dependence is well explained with theoretical calculations by the weak-field asymptotic theory for the 2πhighest occupied molecular orbital (HOMO). On the other hand, the peak angle shifts toward the laser polarization direction as the kinetic energy decreases, indicating that pathways other than direct ionization from the HOMO contribute to the dissociative ionization.

DOI： 10.1103/PhysRevA.100.053422

Probing Rydberg-Rydberg interactions in N<inf>2</inf> by ultrafast EUV-NIR photoelectron spectroscopy Reviewed International coauthorship Open Access

Fushitani, M., Toida, Y., Légaré, F., Hishikawa, A.

Optics Express Vol. 27 ( 14 ) page： 19702 - 19711 2019.7

Coincidence momentum imaging of four- and three-body Coulomb explosion of formaldehyde in ultrashort intense laser fields Reviewed International coauthorship

Chien-Ming Tseng, Mizuho Fushitani, Akitaka Matsuda, Akiyoshi Hishikawa

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 228 page： 25 - 30 2018.10

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Ion-coincidence momentum imaging of Coulomb explosion of formaldehyde (H2CO) in femtosecond intense laser fields (800 nm, 1.3 x 10(15) W/cm(2)) is performed with two different laser pulse durations (7 fs and 35 fs). In the 7-fs laser fields, the full fragmentation pathway from H2CO4+ -> H+ + H+ + C+ + O+ is identified. The angles between the fragment momenta are well reproduced by a simple Coulomb explosion model from the geometry of neutral formaldehyde, showing that the molecular structure is virtually frozen along the bending coordinates during the multiple ionization. Three-body Coulomb explosion pathways from triply charged states, H2CO3+ -> H+ + H+ + C+ + O+, are observed in both the 7-fs and 35-fs laser fields. Significant changes in the momentum angle distribution and asymmetric energy partitioning between two H+ ions are observed in the 35-fs case, which are attributed to structural deformation prior to the Coulomb explosion in the longer pulse.

DOI： 10.1016/j.elspec.2018.07.001

Femtosecond laser filamentation in gaseous ethylene: Formation of hydrogenated amorphous carbon Reviewed

A. Matsuda, T. Hayashi, R. Kitaura, A. Hishikawa

Chem. Lett. Vol. 46 page： 1426-1429 2017.7

Selective bond breaking of CO2 in phase-locked two-color intense laser fields: laser field intensity dependence Reviewed Open Access

Tomoyuki Endo, Hikaru Fujise, Yuuna Kawachi, Ayaka Ishihara, Akitaka Matsuda, Mizuho Fushitani, Hirohiko Kono, Akiyoshi Hishikawa

PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vol. 19 ( 5 ) page： 3550 - 3556 2017.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Selective bond breaking of CO2 in phase-locked omega-2 omega two-color intense laser fields (lambda = 800 nm and 400 nm, total field intensity l similar to 10(14) W cm(-2)) has been investigated by coincidence momentum imaging. The CO+ and O+ fragment ions produced by two-body Coulomb explosion, CO22+ -> CO+ + O+, exhibit asymmetric distributions along the laser polarization direction, showing that one of the two equivalent C-O bonds is selectively broken by the laser fields. At a field intensity higher than 2 x 10(14) W cm(-2), the largest fragment asymmetry is observed when the relative phase phi between the omega and 2 omega laser fields is similar to 0 and pi. On the other hand, an increase of the asymmetry and a shift of the phase providing the largest asymmetry are observed at lower field intensities. The selective bond breaking and its dependence on the laser field intensity are discussed in terms of a mechanism involving deformation of the potential energy surfaces and electron recollision in intense laser fields.

DOI： 10.1039/c6cp07471e

Single-order laser high harmonics in XUV for ultrafast photoelectron spectroscopy of molecular wavepacket dynamics Reviewed Open Access

Fushitani, M., Hishikawa, A.

Structural Dynamics Vol. 3 ( 6 ) page： 062602 2016.11

Imaging Electronic Excitation of NO by Ultrafast Laser Tunneling Ionization Reviewed

Tomoyuki Endo, Akitaka Matsuda, Mizuho Fushitani, Tomokazu Yasuike, Oleg I. Tolstikhin, Toru Morishita, Akiyoshi Hishikawa

PHYSICAL REVIEW LETTERS Vol. 116 ( 16 ) page： 163002 2016.4

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Tunneling-ionization imaging of photoexcitation of NO has been demonstrated by using few-cycle near-infrared intense laser pulses (8 fs, 800 nm, 1.1 x 10(14) W/cm(2)). The ion image of N+ fragment ions produced by dissociative ionization of NO in the ground state, NO (X-2 Pi; 2 pi) -> NO+ + e(-) -> N+ + O + e(-), exhibits a characteristic momentum distribution peaked at 45 degrees with respect to the laser polarization direction. On the other hand, a broad distribution centered at similar to 0 degrees appears when the A(2)Sigma(+) (3s sigma) excited state is prepared as the initial state by deep-UV photoexcitation. The observed angular distributions are in good agreement with the corresponding theoretical tunneling ionization yields, showing that the fragment anisotropy reflects changes of the highest-occupied molecular orbital by photoexcitation.

DOI： 10.1103/PhysRevLett.116.163002

Photoelectron sidebands induced by a chirped laser field for shot-by-shot temporal characterization of FEL pulses Reviewed

Chien-Nan Liu, Toru Morishita, Mizuho Fushitani, Akiyoshi Hishikawa

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 49 ( 3 ) page： 034005 2016.2

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We theoretically investigate the laser-assisted photoionization of He by an extreme ultra violet (XUV) pulse in the presence of a linearly chirped intense laser pulse by solving the time-dependent Schrodinger equation within the single-active-electron approximation. Analysis based on the time-dependent perturbation theory is also carried out to provide more physical insights. A new scheme is shown to be capable of extracting the arrival time of an XUV free-electron laser (FEL) pulse relative to an external laser pulse as well as the XUV pulse duration from the photoelectron sidebands resulting from XUV ionization in the presence of a chirped laser pulse. This scheme is independent of the energy fluctuation and the timing jittering of the FEL pulse. Therefore it can be implemented in a non-invasive way to characterize FEL pulses on a shot-by-shot basis in time-resolved spectroscopy.

DOI： 10.1088/0953-4075/49/3/034005

Coincidence momentum imaging of asymmetric Coulomb explosion of CO2 in phase-locked two-color intense laser fields Reviewed

Tomoyuki Endo, Hikaru Fujise, Akitaka Matsuda, Mizuho Fushitani, Hirohiko Kono, Akiyoshi Hishikawa

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 207 page： 50 - 54 2016.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Coulomb explosion of CO2, CO2 -> CO2+2 + 2e(-) -> CO+ + O +2e(-), in phase-locked two-color ultrashort intense laser fields (800 nm and 400 nm, similar to 10(14) W/cm(2)) has been investigated by coincidence momentum imaging. The momentum images of the O+ and CO+ fragments show asymmetric distributions along the laser polarization direction depending on the relative phase of the two-color laser fields. The fragment asymmetry becomes most prominent (similar to 4%) at the relative phases providing the largest asymmetry of the electric field amplitude, with the O+ fragments preferentially ejected to the stronger field side. The mechanism of the asymmetric bond breaking of the two equivalent C-O bonds is discussed in terms of the nuclear dynamics in CO22+. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2015.12.010

Femtosecond two-photon Rabi oscillations in excited He driven by ultrashort intense laser fields Reviewed

M. Fushitani, C. -N. Liu, A. Matsuda, T. Endo, Y. Toida, M. Nagasono, T. Togashi, M. Yabashi, T. Ishikawa, Y. Hikosaka, T. Morishita, A. Hishikawa

NATURE PHOTONICS Vol. 10 ( 2 ) page： 102 - + 2016.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Coherent light-matter interaction provides powerful methods for manipulating quantum systems(1-3). Rabi oscillation is one such process. As it enables complete population transfer to a target state, it is thus routinely exploited in a variety of applications in photonics, notably quantum information processing(4,5). The extension of coherent control techniques to the multiphoton regime offers wider applicability, and access to highly excited or dipole-forbidden transition states. However, the multiphoton Rabi process is often disrupted by other competing nonlinear effects such as the a.c. Stark shift, especially at the high laser-field intensities necessary to achieve ultrafast Rabi oscillations(6). Here we demonstrate a new route to drive two-photon Rabi oscillations on timescales as short as tens of femtoseconds, by utilizing the strong-field phenomenon known as Freeman resonance(7). The scenario is not specific to atomic helium as investigated in the present study, but broadly applicable to other systems, thus opening new prospects for the ultrafast manipulation of Rydberg states(8).

DOI： 10.1038/NPHOTON.2015.228

Correlation between Photoeletron and Photoion in Ultrafast Multichannel Photoionization of Ar Reviewed

R. Itakura, M. Fushitani, A. Hishikawa, T. Sako

INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2015 (ICCMSE 2015) Vol. 1702 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

We theoretically investigate coherent dynamics of ions created through ultrafast multichannel photoionization from a viewpoint of photoelectron-photoion correlation. The model calculation on single-photon ionization of Ar reveals that the coherent hole dynamics in Ar+ associated with a superposition of the spin-orbit states P-2(J) (J = 3/2 and 1/2) can be identified by monitoring only the photoion created by a Fourier-transform limited extreme ultraviolet (EUV) pulse with the 9-fs pulse duration, while the coherence is lost by a chirped EUV pulse. It is demonstrated that by coincidence detection of the photoelectron and photoion the coherent hole dynamics can be extracted even in the case of ionization by a chirped EUV pulse with the sufficiently wide bandwidth.

DOI： 10.1063/1.4938829

Ion-Coincidence Momentum Imaging of Three-Body Coulomb Explosion of Formaldehyde in Ultrashort Intense Laser Fields Reviewed

M. Fushitani, C-M. Tseng, A. Matsuda, A. Hishikawa

INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2015 (ICCMSE 2015) Vol. 1702 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Three-body Coulomb explosion of formaldehyde (H2CO) in intense 7- and 35-fs laser fields (1.3 x 10(15) W/cm(2)) has been investigated by using ion-coincidence momentum imaging technique. Two types of explosion pathways from the triply charged state, H2CO3+ -> (i) H+ + H+ + CO+ and (ii) H+ + CH+ + O+, have been identified. It is shown from the momentum correlation of the fragment ions of pathway (i), that the geometrical structure of the molecule is essentially frozen along the H-C-H bending coordinate for the 7-fs case. On the other hand, for a longer pulse duration (35 fs), structural deformation along the C-H stretching and H-C-H bending coordinates is identified, which is ascribed to the nuclear dynamics in the dication states populated within the laser pulse duration.

DOI： 10.1063/1.4938821

Fragment anisotropy on dissociative ionization of NO in two-color intense laser fields Reviewed

Tomoyuki Endo, Ayaka Ishihara, Akitaka Matsuda, Mizuho Fushitani, Akiyoshi Hishikawa

XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12 Vol. 635 ( 11 ) 2015

Language：Japanese Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

Dissociative-ionization of NO, NO -> NO+ + e(-) -> N+ + O + e(-), in omega-2 omega two-color phase-controlled intense laser fields was investigated by three-dimensional ion momentum imaging. The moment Urn image of the N+ ion exhibited anisotropic distributions peaked at 35 degrees against the laser polarization, which show clear left-right asymmetry depending on the omega-2 omega relative phase. The present study demonstrates that the molecular orbital can be retrieved by distinguishing the difference between the N and O side from the fragment anisotropy by intense laser pulses.

DOI： 10.1088/1742-6596/635/11/112027

Determination of Absolute Cross-Sections of Nonresonant EUV-UV Two-Color Two-Photon Ionization of He Reviewed

M. Fushitani, Y. Hikosaka, A. Matsuda, T. Endo, E. Shigemasa, M. Nagasono, T. Sato, T. Togashi, M. Yabashi, T. Ishikawa, A. Hishikawa

ULTRAFAST PHENOMENA XIX Vol. 162 page： 109 - 112 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPRINGER-VERLAG BERLIN

Single-shot photoelectron spectroscopy was performed for nonresonant EUV-UV two-color two-photon ionization of He. From data analysis on the shot-by-shot basis, the absolute cross-section was determined to be sigma((2))(59.7 nm, 268 nm) = 4.1(6) x 10(-52) cm(4) s.

DOI： 10.1007/978-3-319-13242-6_26

Time-Resolved Coulomb Explosion Imaging of Ultrafast Fragmentation of CS2 in Highly Charged States Reviewed

Akitaka Matsuda, Eiji J. Takahashi, Akiyoshi Hishikawa

ULTRAFAST PHENOMENA XIX Vol. 162 page： 168 - 171 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPRINGER-VERLAG BERLIN

Time-resolved three-body Coulomb explosion imaging of dissociating CS2 in few-cycle intense laser fields (9 fs, 4 x 10(15) W/cm(2)) is performed. It is revealed that the ultrafast fragmentation dynamics of CS2 in highly charged states proceed in a different timescale depending on the charge state.

DOI： 10.1007/978-3-319-13242-6_40

Ultrafast two-photon Rabi oscillations in excited He driven by femtosecond intense laser fields Reviewed

A. Hishikawa, M. Fushitani, C. N. Liu, A. Matsuda, T. Endo, Y. Toida, Y. Hikosaka, T. Morishita

XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12 Vol. 635 ( 9 ) 2015

Language：Japanese Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

We demonstrate ultrafast multiphoton coherent excitation in near-infrared intense laser fields (<= 10 TW/cm(2)) using excited helium in the 1s2p (P-1) state as the target. Strong two-photon coupling between the 2p state and the 5f and 6f Rydberg states drives ultrafast Rabi oscillations in tens of femtosecond. Theoretical calculations solving the time-dependent Schrodinger equation were carried out to elucidate the strong field effects.

DOI： 10.1088/1742-6596/635/9/092082

Five-photon sequential double ionization of He in intense extreme-ultraviolet free-electron laser fields Reviewed

Y. Hikosaka, M. Fushitani, A. Matsuda, T. Endo, Y. Toida, E. Shigemasa, M. Nagasono, K. Tono, T. Togashi, M. Yabashi, T. Ishikawa, A. Hishikawa

PHYSICAL REVIEW A Vol. 90 ( 5 ) page： 053403 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

A multiphoton ionization process of He in intense extreme ultraviolet free-electron laser fields is investigated in a photon energy range of hv = 20.1-20.8 eV using shot-by-shot photoelectron spectroscopy. A photoelectron peak resulting from sequential double ionization of He due to five-photon absorption is observed around hv = 20.4. Shot-by-shot analysis of photoelectron spectra shows that two-photon resonance to the He+(2s S-2) state from the He+ ground state is responsible for the substantial enhancement of five-photon double ionization. Effective cross sections for two-photon absorption between the 1s and 2s states of He+ and for one-photon absorption from the He+ 2s state are obtained.

DOI： 10.1103/PhysRevA.90.053403

Photoelectron-photoion correlation in ultrafast multichannel photoionization of Ar Reviewed

R. Itakura, M. Fushitani, A. Hishikawa, T. Sako

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 47 ( 19 ) page： 195602 2014.10

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

Ultrafast multichannel single-photon ionization of Ar is investigated theoretically by a model calculation incorporating correlation between the photoelectron and photoion. It is shown that the coherent hole dynamics in Ar+ associated with a superposition of the spin-orbit states can be observed by using a Fourier-transform limited laser pulse for ionization, while the coherence is degraded or lost by chirped a laser pulse. We demonstrate that the coherent hole dynamics can be retrieved even in the case of ionization by a chirped laser pulse, by labeling the photoion dynamics with the counterpart photoelectron energy.

DOI： 10.1088/0953-4075/47/19/195602

Time-resolved laser Coulomb explosion imaging using few-cycle intense laser pulses: Application to exploding CS2 in highly charged states Reviewed

Akitaka Matsuda, Eiji J. Takahashi, Akiyoshi Hishikawa

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 195 page： 327 - 331 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER

Ion-coincidence momentum imaging of three-body Coulomb explosion of CS2, CS2z+ -> Sp+ + Cq+ + Sr+ (z = p + q + r), in few-cycle intense laser fields (9 fs, similar to 10(15) W/cm(2)) is presented. It is shown that the momentum distributions of fragment ions produced from CS210+ are well reproduced by a classical explosion model incorporating the coordinate and momentum distributions of the initial ground vibrational state of CS2. On the other hand, a significant deviation is observed for CS23+ due to the non-Coulombic character of the potential energy surfaces. Coulomb explosion imaging is applied to real-time probing of Coulomb exploding CS2 in highly charged states, using a pair of intense few-cycle laser pulses. It is shown that the explosion proceeds in a different time scale depending on the charge state, mostly along the linear geometry during the bond-breaking of the two C S bonds. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2013.12.011

Preface Reviewed

Hiroshi Daimon, Akiyoshi Hishikawa, Catalin Miron

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 195 page： 285 - 286 2014.8

Special issue on ultrafast electron and molecular dynamics Preface Reviewed Open Access

Fernando Martin, Akiyoshi Hishikawa, Marc Vrakking

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 47 ( 12 ) 2014.6

Dissociative ionization of NO in few-cycle intense laser fields : Effects of pi-sigma electronic transition Reviewed

Tomoyuki Endo, Mizuho Fushitani, Akitaka Matsuda, Akiyoshi Hishikawa

XXVIII INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS (ICPEAC) Vol. 488 ( SECTION 3 ) 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

Dissociative ionization (DI) of NO in few-cycle intense laser fields was investigated by using the 3D momentum imaging method. It was found that the symmetry change in the outermost occupied molecular orbital upon the pi - sigma electronic transition is clearly reflected in the spatial anisotropy of the fragment ion, N+.

DOI： 10.1088/1742-6596/488/3/032025

Resolving the enhanced nonlinear double excitation of helium in intense ultra-short extreme-ultraviolet pulses Reviewed

Chien-Nan Liu, Akiyoshi Hishikawa, Toru Morishita

XXVIII INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS (ICPEAC) Vol. 488 ( SECTION 3 ) 2014

Language：Japanese Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

We present a theoretical study for multiphoton double excitation of He atoms exposed to an intense ultrashort extreme-ultraviolet (EUV) pulse, where the photon energy coincides with the transition energy from the ground state to a Rydberg state. We identify the mechanism of the enhanced three-photon absorption probability as observed in the experiment.

DOI： 10.1088/1742-6596/488/3/032047

Two-photon rabi oscillations of excited he atoms in ultrafast strong laser field ionization Reviewed

Fushitani M, Liu C.-N, Matsuda A, Endo T, Toida Y, Hikosaka Y, Nagasono M, Togashi T, Yabashi M, Ishikawa T, Morishita T, Hishikawa A

Optics InfoBase Conference Papers 2014

Determination of absolute cross-sections of nonresonant EUV-UV two-color two-photon ionization of he

M. Fushitani, Y. Hikosaka, A. Matsuda, T. Endo, E. Shigemasa, M. Nagasono, T. Sato, T. Togashi, M. Yabashi, T. Ishikawa, A. Hishikawa

Optics InfoBase Conference Papers 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Optical Society of America (OSA)

Single-shot photoelectron spectroscopy was performed for nonresonant EUV-UV twocolor two-photon ionization of He. From data analysis on the shot-by-shot basis, the absolute cross-section was determined to be σ(2)(597nm, 268nm) = 4.1(6)×10-52 cm4 s. © 2014 OSA.

DOI： 10.1364/up.2014.08.tue.p2.5

Ultrafast photoelectron spectroscopy of electron-ion wave packets in Rydberg N2

M. Fushitani, Y. Toida, F. Légaré, A. Hishikawa

Optics InfoBase Conference Papers 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Optical Society of America (OSA)

Time-resolved photoelectron spectroscopy of N2 Rydberg using single-order high harmonics at 80 nm reveals ultrafast wavepacket dynamics (~3 fs) of both Rydberg electron and the corresponding N2 + core as the beating oscillation (~ 300 fs). © 2014 OSA.

DOI： 10.1364/up.2014.07.mon.p1.5

Ultrafast coulomb explosion of formaldehyde in 7 and 35 fs intense laser fields studied by triple ion-coincidence momentum imaging

Chien-Ming Tseng, Akitaka Matsuda, Mizuho Fushitani, Akiyoshi Hishikawa

Optics InfoBase Conference Papers 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Optical Society of America (OSA)

Ultrafast three-body Coulomb explosion of formaldehyde (H2CO) in intense laser fields has been studied. The pulse duration dependence of the Newton plot of the fragment ions revealed the ultrafast molecular dynamics in the dication states. © 2014 OSA.

DOI： 10.1364/up.2014.09.wed.p3.23

Two-photon rabi oscillations of excited he atoms in ultrafast strong laser field ionization

Fushitani M., Liu C.N., Matsuda A., Endo T., Toida Y., Hikosaka Y., Nagasono M., Togashi T., Yabashi M., Ishikawa T., Morishita T., Hishikawa A.

Optics InfoBase Conference Papers 2014

Time-resolved Coulomb explosion imaging of ultrafast fragmentation of CS2 in highly charged states

Akitaka Matsuda, Eiji J. Takahashi, Akiyoshi Hishikawa

Optics InfoBase Conference Papers 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Optical Society of America (OSA)

Time-resolved Coulomb explosion imaging of CS2 in few-cycle intense laser fields revealed that the ultrafast fragmentation dynamics of CS2 in highly charged states proceed in a different timescale depending on the charge state. © 2014 OSA.

DOI： 10.1364/up.2014.08.tue.p2.18

Nonresonant EUV-UV two-color two-photon ionization of He studied by single-shot photoelectron spectroscopy Reviewed

M. Fushitani, Y. Hikosaka, A. Matsuda, T. Endo, E. Shigemasa, M. Nagasono, T. Sato, T. Togashi, M. Yabashi, T. Ishikawa, A. Hishikawa

PHYSICAL REVIEW A Vol. 88 ( 6 ) page： 063422 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Single-shot photoelectron spectroscopy of nonresonant two-color two-photon ionization of He has been carried out using an intense free-electron laser (FEL) at 59.7 nm and a femtosecond UV laser at 268 nm. By shot-by-shot analysis of photoelectron spectra, the cross section for nonresonant two-color ionization of He is determined to be sigma((2)) = 4.1(6) x 10(-52) cm(4) s. The cross-correlation trace derived from the nonresonant signals shows that the temporal resolution of the system is 0.36(3) ps, which is mainly governed by the timing jitter between the FEL and UV laser pulses.

DOI： 10.1103/PhysRevA.88.063422

Compact XFEL and AMO sciences: SACLA and SCSS Reviewed

M. Yabashi, H. Tanaka, T. Tanaka, H. Tomizawa, T. Togashi, M. Nagasono, T. Ishikawa, J. R. Harries, Y. Hikosaka, A. Hishikawa, K. Nagaya, N. Saito, E. Shigemasa, K. Yamanouchi, K. Ueda

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 46 ( 16 ) page： 164001 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The concept, design and performance of Japan's compact free-electron laser (FEL) facilities, the SPring-8 Compact SASE Source test accelerator (SCSS) and SPring-8 Angstrom Compact free electron LAser (SACLA), and their applications in mainly atomic, molecular and optical science are reviewed. At SCSS, intense, ultrafast FEL pulses at extreme ultraviolet (EUV) wavelengths have been utilized for investigating various multi-photon processes in atoms, molecules and clusters by means of ion and electron spectroscopy. The quantum optical effect superfluorescence has been observed with EUV excitation. A pump-probe technique combining FEL pulses with near infrared laser pulses has been realized to study the ultrafast dynamics of atoms, molecules and clusters in the sub-picosecond regime. At SACLA, deep inner-shell multi-photon ionization by intense x-ray FEL pulses has been investigated. The development of seeded FEL sources for producing transversely and temporally coherent light, as well as the expected impact on advanced science are discussed.

DOI： 10.1088/0953-4075/46/16/164001

Resonances in three-photon double ionization of Ar in intense extreme ultraviolet free-electron laser fields studied by shot-by-shot photoelectron spectroscopy Reviewed

Y. Hikosaka, M. Fushitani, A. Matsuda, T. Endo, Y. Toida, E. Shigemasa, M. Nagasono, K. Tono, T. Togashi, M. Yabashi, T. Ishikawa and A. Hishikawa

Phys. Rev. A Vol. 88 ( 023421 ) page： 023421 2013.8

Resonances in three-photon double ionization of Ar in intense extreme-ultraviolet free-electron laser fields studied by shot-by-shot photoelectron spectroscopy Reviewed

Y. Hikosaka, M. Fushitani, A. Matsuda, T. Endo, Y. Toida, E. Shigemasa, M. Nagasono, K. Tono, T. Togashi, M. Yabashi, T. Ishikawa, A. Hishikawa

PHYSICAL REVIEW A Vol. 88 ( 2 ) 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Shot-by-shot photoelectron spectroscopy has been performed to study the three-photon double ionization of Ar in intense extreme-ultraviolet free-electron laser fields over a photon energy range of 19.6-22.0 eV. It is found that the double ionization to Ar2+ 3p(-2) proceeds sequentially via the formation of singly charged Ar+ 3p(-1) states and is enhanced around photon energies of 20.5 and 21.5 eV. Two types of resonance are identified in the two-photon ionization of the Ar+ 3p(-1) states: (i) resonances to intermediate states at the one-photon energy level and (ii) those to autoionizing states above the Ar2+ ionization threshold.

DOI： 10.1103/PhysRevA.88.023421

Time-resolved four-body coulomb explosion imaging of correlated dynamics of hydrogen atoms in acetylene dication Reviewed Open Access

A. Matsuda, M. Fushitani, E. J. Takahashi, A. Hishikawa

EPJ Web of Conferences Vol. 41 2013

Language：English Publishing type：Research paper (international conference proceedings)

The correlated motion of the two deuterium atoms associated with the hydrogen migration and structural deformation to non-planar geometry are identified in acetylene dication by the time-resolved four-body Coulomb explosion imaging. © Owned by the authors, published by EDP Sciences, 2013.

DOI： 10.1051/epjconf/20134102013

Ultrafast nonlinear double excitations of he in intense EUV FEL fields Reviewed Open Access

M. Fushitani, Y. Hikosaka, A. Matsuda, C. N. Liu, T. Morishita, E. Shigemasa, A. Hishikawa

EPJ Web of Conferences Vol. 41 2013

Language：English Publishing type：Research paper (international conference proceedings)

Three-photon double excitation of He in intense EUV FEL fields is studied by the shot-by-shot photoelectron spectroscopy, revealing the enhancement by resonances to the doubly excited states converging to the He+ N=3 level. © Owned by the authors, published by EDP Sciences, 2013.

DOI： 10.1051/epjconf/20134102009

Shot-by-Shot Photoelectron Spectroscopy of Rare Gas Atoms in Ultrashort Intense EUV Free-Electron Laser Fields

Mizuho Fushitani, Yasumasa Hikosaka, Akitaka Matsuda, Eiji Shigemasa, Akiyoshi Hishikawa

Springer Series in Chemical Physics page： 151 - 163 2013

Two-electron dynamics in nonlinear double excitation of helium by intense ultrashort extreme-ultraviolet pulses Reviewed

Chien-Nan Liu, Akiyoshi Hishikawa, Toru Morishita

PHYSICAL REVIEW A Vol. 86 ( 5 ) page： 13 2012.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We present a theoretical study for multiphoton double excitation of He atoms exposed to an intense ultrashort extreme-ultraviolet (EUV) pulse, where the photon energy coincides with the transition energy from the ground state to a Rydberg state, by solving the time-dependent Schrodinger equation in the hyperspherical coordinates. Photoelectron spectra under the conditions comparable with a recent experiment [Hishikawa et al., Phys. Rev. Lett. 107, 243003 (2011)] are calculated and analyzed. We identify the mechanism of the enhanced three-photon absorption probability which is more than one order of magnitude larger than that for the two-photon process in accordance with the experiment. The enhancement is attributed to a propensity rule for double excitation in a two-step mechanism, in which a one-photon absorption by one electron to a Rydberg state is followed by a two-photon absorption by the other electron to an excited orbital, while the first electron remains at nearly the same principle quantum number. Based on the time-dependent perturbation theory, the three-photon absorption probability exhibits peculiar cubic dependence on the pulse duration due to the propensity rule, in contrast to the linear dependence of the two-photon absorption probability. Thus a crossover between the two-and three-photon absorption probabilities takes place for sufficiently intense and long pulses. We also study the time evolution of a doubly excited two-electron wave packet created by an intense ultrashort EUV pulse efficiently using the same enhancement scheme, opening up the possibility of visualizing the correlated motion of two electrons in the time domain.

DOI： 10.1103/PhysRevA.86.053426

レーザークーロン爆発イメージングによる実時間反応追跡 Invited Reviewed

菱川明栄

レーザー研究 Vol. 40 page： 745-751 2012.10

EUV and soft X-ray photoelectron spectroscopy of isolated atoms and molecules using single-order laser high-harmonics at 42 eV and 91 eV Reviewed

M. Fushitani, A. Matsuda and A. Hishikawa

J. Electron. Spectrosc. Relat. Phenom. Vol. 184 page： 561-568 2012.2

極紫外自由電子レーザー場における原子のシングルショット光電子分光 Invited Reviewed

彦坂泰正，伏谷瑞穂，菱川明栄

しょうとつ Vol. 9 ( 1 ) page： 5-10 2012.1

EUV and soft X-ray photoelectron spectroscopy of isolated atoms and molecules using single-order laser high-harmonics at 42 eV and 91 eV Reviewed

Mizuho Fushitani, Akitaka Matsuda, Akiyoshi Hishikawa

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 184 ( 11-12 ) page： 561 - 568 2012.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Photoelectron spectroscopy of isolated atoms and molecules using single-order high-harmonics of Ti:Sapphire laser pulses (800 nm, 12 fs/30 fs) is demonstrated. Dielectric multilayer mirrors, SiC/Mg and Mo/Si, are used to isolate the 27th (42 eV) and 59th (91 eV) order harmonics, respectively. The obtained harmonics are characterized by valence and inner-shell photoelectron spectroscopy of Xe. The applications to two-color two-photon ionization of He and pump-probe spectroscopy of ultrafast photodissociation of Br-2, Br-2(C-1 Pi(u)) --> Br(P-2(3/2))+ Br(P-2(3/2)), are presented. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2011.10.002

Theoretical study of multi-photon double electron excitation of He by intense ultrashort EUV pulses Reviewed

Chien-Nan Liu, Toru Morishita, Shinichi Watanabe, Akiyoshi Hishikawa

XXVII INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS (ICPEAC 2011), PTS 1-15 Vol. 388 ( PART 3 ) 2012

Language：Japanese Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

We use the time-dependent hypersperhical close-coupling method to study the double excitation of helium atoms by intense ultrashort XUV pulses. In addition to showing the photoelectron yield spectra, we demonstrate that free electron lasers can be used to efficiently create doubly excited electron wave packets, opening up the possibility of visualizing the correlated motion of electrons in atoms.

DOI： 10.1088/1742-6596/388/3/032007

Visualizing correlated dynamics of hydrogen atoms in acetylene dication by time-resolved four-body coulomb explosion imaging Reviewed

Akitaka Matsuda, Mizuho Fushitani, Eiji J. Takahashi, Akiyoshi Hishikawa

Springer Proceedings in Physics Vol. 125 page： 317 - 322 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Springer Science and Business Media, LLC

Ultrafast hydrogenmigration in deuterated acetylene dication (C 2D2+2 ) is studied by time-resolved four-body Coulomb explosion imaging, C2D4+ 2 → D++ C ++ C ++ D +, using a pair of few-cycle intense laser pulses (9 fs, 1.3 × 1014 W/cm 2). Momentum correlation of the D+ ions produced by the full fragmentation process shows that (1) motions of the two deuterium atoms are strongly correlated during the isomerization and (2) the molecular structure deforms to nonplanar geometries. © Springer-Verlag Berlin Heidelberg 2012.

DOI： 10.1007/978-3-642-28948-4_53

Enhanced Nonlinear Double Excitation of He in Intense Extreme Ultraviolet Laser Fields Reviewed

A. Hishikawa, M. Fushitani, Y. Hikosaka, A. Matsuda, C. -N. Liu, T. Morishita, E. Shigemasa, M. Nagasono, K. Tono, T. Togashi, H. Ohashi, H. Kimura, Y. Senba, M. Yabashi, T. Ishikawa

PHYSICAL REVIEW LETTERS Vol. 107 ( 24 ) page： 243003 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Nonlinear, three-photon double excitation of He in intense extreme ultraviolet free-electron laser fields (similar to 24.1 eV, similar to 5 TW/cm(2)) is presented. Resonances to the doubly excited states converging to the He(+) N = 3 level are revealed by the shot-by-shot photoelectron spectroscopy and identified by theoretical calculations based on the time-dependent Schrodinger equation for the two-electron atom under a laser field. It is shown that the three-photon double excitation is enhanced by intermediate Rydberg states below the first ionization threshold, giving a greater contribution to the photoionization yields than the two-photon process by more than 1 order of magnitude.

DOI： 10.1103/PhysRevLett.107.243003

クーロン爆発イメージングによる超高速反応追跡 Invited

菱川明栄

光アライアンス Vol. 22 ( 11 ) page： 19-22 2011.11

光のゆらぎで探る：自由電子レーザー場中の原子 Invited

伏谷瑞穂, 彦坂泰正, 菱川明栄

光アライアンス Vol. 22 ( 10 ) page： 25-28 2011.10

A magnetic-bottle multi-electron-ion coincidence spectrometer Reviewed

Akitaka Matsuda, Mizuho Fushitani, Chien-Ming Tseng, Yasumasa Hikosaka, John H. D. Eland, Akiyoshi Hishikawa

REVIEW OF SCIENTIFIC INSTRUMENTS Vol. 82 ( 10 ) page： 103105 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

A novel multi-electron-ion coincidence spectrometer developed on the basis of a 1.5 m-long magnetic-bottle electron spectrometer is presented. Electrons are guided by an inhomogeneous magnetic field to a detector at the end of the flight tube, while a set of optics is used to extract counterpart ions to the same detector, by a pulsed inhomogeneous electric field. This setup allows ion detection with high mass resolution, without impairing the high collection efficiency for electrons. The performance of the coincidence spectrometer was tested with double ionization of carbon disulfide, CS2 -> CS22+ + e(-) + e(-), in ultrashort intense laser fields (2.8 x 10(13) W/cm(2), 280 fs, 1030 nm) to clarify the electron correlation below the rescattering threshold. (C) 2011 American Institute of Physics. [doi:10.1063/1.3648133]

DOI： 10.1063/1.3648133

Time-resolved EUV photoelectron spectroscopy of dissociating I-2 by laser harmonics at 80 nm Reviewed Open Access

Mizuho Fushitani, Akitaka Matsuda, Akiyoshi Hishikawa

OPTICS EXPRESS Vol. 19 ( 10 ) page： 9600 - 9606 2011.5

Language：English Publishing type：Research paper (scientific journal) Publisher：OPTICAL SOC AMER

Generation of single-order laser harmonics in extreme ultraviolet (EUV) and the application to the time-resolved photoelectron spectroscopy of I-2 are demonstrated. The EUV pulses at 80 nm were generated from Kr as the 5th order harmonics of intense 400 nm laser pulses and then separated from other harmonic orders by a thin indium foil. The pump-probe photoelectron spectroscopy of I-2 in the B (3)Pi(0(u)(+)) and B" (1)Pi(1(u)) states excited by visible laser pulses at 490 nm showed a rapid increase in the yield of atomic iodine (similar to 400 fs), reflecting the dissociation dynamics evolving simultaneously in the two excited states. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.009600

Time-resolved EUV photoelectron spectroscopy of dissociating I(2) by laser harmonics at 80 nm Reviewed

Fushitani, M. and Matsuda, A. and Hishikawa, A.

Optics Express Vol. 19 ( 10 ) page： 9600-9606 2011

Language：English Publishing type：Research paper (scientific journal)

Generation of single-order laser harmonics in extreme ultraviolet (EUV) and the application to the time-resolved photoelectron spectroscopy of I(2) are demonstrated. The EUV pulses at 80 nm were generated from Kr as the 5th order harmonics of intense 400 nm laser pulses and then separated from other harmonic orders by a thin indium foil. The pump-probe photoelectron spectroscopy of I(2) in the B (3)Pi(0(u)(+)) and B" (1)Pi(1(u)) states excited by visible laser pulses at 490 nm showed a rapid increase in the yield of atomic iodine (similar to 400 fs), reflecting the dissociation dynamics evolving simultaneously in the two excited states. (C) 2011 Optical Society of America

Visualizing hydrogen atoms migrating in acetylene dication by time-resolved three-body and four-body Coulomb explosion imaging Reviewed

Matsuda, A. and Fushitani, M. and Takahashi, E. J. and Hishikawa, A.

Physical Chemistry Chemical Physics Vol. 13 ( 19 ) page： 8697-8704 2011

Language：English Publishing type：Research paper (scientific journal)

The visualization of ultrafast isomerization of deuterated acetylene dication (C(2)D(2)(2+)) is demonstrated by time-resolved Coulomb explosion imaging with sub-10 fs intense laser pulses ( 9 fs, 0.13 PW cm(-2), 800 nm). The Coulomb explosion imaging monitoring the three-body explosion process, C(2)D(2)(3+) -> D(+) + C(+) + CD(+), as a function of the delay between the pump and probe pulses revealed that the migration of a deuterium atom proceeds in a recurrent manner; One of the deuterium atoms first shifts from one carbon site to the other in a short timescale (similar to 90 fs), and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation. Correlated motion of the two deuterium atoms associated with the hydrogen migration and structural deformation to non-planar geometry are identified by the time-resolved four-body Coulomb explosion imaging, C(2)D(2)(4+) - D(+) + C(+) + C(+) + D(+).

DOI： Doi 10.1039/C0cp02333g

Visualizing hydrogen atoms migrating in acetylene dication by time-resolved three-body and four-body Coulomb explosion imaging Reviewed

Akitaka Matsuda, Mizuho Fushitani, Eiji J. Takahashi, Akiyoshi Hishikawa

PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vol. 13 ( 19 ) page： 8697 - 8704 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

The visualization of ultrafast isomerization of deuterated acetylene dication (C2D22+) is demonstrated by time-resolved Coulomb explosion imaging with sub-10 fs intense laser pulses ( 9 fs, 0.13 PW cm(-2), 800 nm). The Coulomb explosion imaging monitoring the three-body explosion process, C2D23+ -> D+ + C+ + CD+, as a function of the delay between the pump and probe pulses revealed that the migration of a deuterium atom proceeds in a recurrent manner; One of the deuterium atoms first shifts from one carbon site to the other in a short timescale (similar to 90 fs), and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation. Correlated motion of the two deuterium atoms associated with the hydrogen migration and structural deformation to non-planar geometry are identified by the time-resolved four-body Coulomb explosion imaging, C2D24+ - D+ + C+ + C+ + D+.

DOI： 10.1039/c0cp02333g

EUV SASE-FELを用いた原子の多光子多重イオン化過程の研究 Invited Reviewed

彦坂泰正, 伏谷瑞穂, 菱川明栄

放射光 Vol. 23 ( 5 ) page： 291-294 2010.9

Multiphoton Double Ionization of Ar in Intense Extreme Ultraviolet Laser Fields Studied by Shot-by-Shot Photoelectron Spectroscopy Reviewed

Y. Hikosaka, M. Fushitani, A. Matsuda, C-M. Tseng, A. Hishikawa, E. Shigemasa, M. Nagasono, K. Tono, T. Togashi, H. Ohashi, H. Kimura, Y. Senba, M. Yabashi, T. Ishikawa

PHYSICAL REVIEW LETTERS Vol. 105 ( 13 ) 2010.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Photoelectron spectroscopy has been performed to study the multiphoton double ionization of Ar in an intense extreme ultraviolet laser field (h nu similar to 21 eV, similar to 5 TW/cm(2)), by using a free electron laser (FEL). Three distinct peaks identified in the observed photoelectron spectra clearly show that the double ionization proceeds sequentially via the formation of Ar(+): Ar + h nu -> Ar(+) + e(-) and Ar(+) + 2h nu -> Ar(2+) + e(-). Shot-by-shot recording of the photoelectron spectra allows simultaneous monitoring of FEL spectrum and the multiphoton process for each FEL pulse, revealing that the two-photon ionization from Ar(+) is significantly enhanced by intermediate resonances in Ar(+).

DOI： 10.1103/PhysRevLett.105.133001

Multiphoton Double Ionization of Ar in Intense Extreme Ultraviolet Laser Fields Studied by Shot-by-Shot Photoelectron Spectroscopy Reviewed

Hikosaka, Y. and Fushitani, M. and Matsuda, A. and Tseng, C. M. and Hishikawa, A. and Shigemasa, E. and Nagasono, M. and Tono, K. and Togashi, T. and Ohashi, H. and Kimura, H. and Senba, Y. and Yabashi, M. and Ishikawa, T.

Physical Review Letters Vol. 105 ( 13 ) page： 133001 2010

Language：English Publishing type：Research paper (scientific journal)

Photoelectron spectroscopy has been performed to study the multiphoton double ionization of Ar in an intense extreme ultraviolet laser field (h nu similar to 21 eV, similar to 5 TW/cm(2)), by using a free electron laser (FEL). Three distinct peaks identified in the observed photoelectron spectra clearly show that the double ionization proceeds sequentially via the formation of Ar(+): Ar + h nu -> Ar(+) + e(-) and Ar(+) + 2h nu -> Ar(2+) + e(-). Shot-by-shot recording of the photoelectron spectra allows simultaneous monitoring of FEL spectrum and the multiphoton process for each FEL pulse, revealing that the two-photon ionization from Ar(+) is significantly enhanced by intermediate resonances in Ar(+).

DOI： Doi 10.1103/Physrevlett.105.133001

Multiple Explosion Pathways of the Deuterated Benzene Trication in 9-fs Intense Laser Fields Reviewed

Akitaka Matsuda, Mizuho Fushitani, Richard A. Thomas, Vitali Zhaunerchyk, Akiyoshi Hishikawa

JOURNAL OF PHYSICAL CHEMISTRY A Vol. 113 ( 11 ) page： 2254 - 2260 2009.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The fragmentation of deuterated benzene (CA) in ultrashort intense laser fields (9 fs, 1 x 10(15) W/cm(2)) is studied by the ion-coincidence momentum imaging technique. Five two-body and eight three-body Coulomb explosion pathways from the trication (C6D63+), associated with the deprotonation and ring-opening reactions, are identified. It is found from the fragment momentum correlation that all the observed three-body explosion processes proceed sequentially via the two-body Coulomb explosion forming molecular dications, CmDn2+, with (m,n) = (6,5), (5,5), (5,4), (4,4), (4,3), and (3,3), which further dissociate into pairs of monocations. The branching ratio of the fragmentation pathways estimated from the number of the observed coincidence events indicates that the fragmentation is nonstatistical.

DOI： 10.1021/jp806466x

Electron-ion coincidence momentum imaging of molecular dissociative ionization in intense laser fields: Application to CS2 Reviewed

Akitaka Matsuda, Mizuho Fushitani, Akiyoshi Hishikawa

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 169 ( 2-3 ) page： 97 - 101 2009.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER

An electron-ion coincidence momentum imaging apparatus has been developed and applied to dissociative ionization of CS2 in ultrashort intense laser fields. Photoelectron images of CS2 in 35 fs intense laser fields (2 x 10(13) W/cm(2), 800 nm, linearly polarized) recorded in coincidence with the parent ion, CS2+, show clear concentric ring patterns due to the above-threshold ionization (ATI) process. On the other hand, broad structureless distributions elongated along the direction of the laser polarization are observed in the coincidence electron images for the CS+ and S' fragment ions. The difference in the electron images indicates that the dissociative ionization does not proceed sequentially by the formation and photodissociation of CS2+ in intense laser fields. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2008.12.004

Electron-ion coincidence momentum imaging of molecular dissociative ionization in intense laser fields: Application to CS(2) Reviewed

Matsuda, A. and Fushitani, M. and Hishikawa, A.

Journal of Electron Spectroscopy and Related Phenomena Vol. 169 ( 2-3 ) page： 97-101 2009

Language：English Publishing type：Research paper (scientific journal)

An electron-ion coincidence momentum imaging apparatus has been developed and applied to dissociative ionization of CS(2) in ultrashort intense laser fields. Photoelectron images of CS(2) in 35 fs intense laser fields (2 x 10(13) W/cm(2), 800 nm, linearly polarized) recorded in coincidence with the parent ion, CS(2)(+), show clear concentric ring patterns due to the above-threshold ionization (ATI) process. On the other hand, broad structureless distributions elongated along the direction of the laser polarization are observed in the coincidence electron images for the CS(+) and S' fragment ions. The difference in the electron images indicates that the dissociative ionization does not proceed sequentially by the formation and photodissociation of CS(2)(+) in intense laser fields. (C) 2008 Elsevier B.V. All rights reserved.

Multiple Explosion Pathways of the Deuterated Benzene Trication in 9-fs Intense Laser Fields Reviewed

Matsuda, A. and Fushitani, M. and Thomas, R. A. and Zhaunerchyk, V. and Hishikawa, A.

Journal of Physical Chemistry A Vol. 113 ( 11 ) page： 2254-2260 2009

Language：English Publishing type：Research paper (scientific journal)

The fragmentation of deuterated benzene (CA) in ultrashort intense laser fields (9 fs, 1 x 10(15) W/cm(2)) is studied by the ion-coincidence momentum imaging technique. Five two-body and eight three-body Coulomb explosion pathways from the trication (C(6)D(6)(3+)), associated with the deprotonation and ring-opening reactions, are identified. It is found from the fragment momentum correlation that all the observed three-body explosion processes proceed sequentially via the two-body Coulomb explosion forming molecular dications, C(m)D(n)(2+), with (m,n) = (6,5), (5,5), (5,4), (4,4), (4,3), and (3,3), which further dissociate into pairs of monocations. The branching ratio of the fragmentation pathways estimated from the number of the observed coincidence events indicates that the fragmentation is nonstatistical.

Time-resolved reaction imaging by intense few-cycle laser pulses and laser high-order harmonics Reviewed

M. Fushitani, A. Matsuda, E. J. Takahashi, A. Hishikawa

Journal of Physics: Conference Series Vol. 185 2009

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Physics Publishing

We discuss two novel approaches to visualize ultrafast dynamics of polyatomic molecules using few-cycle intense laser pulses and the high-order harmonics in the soft X-ray region, respectively. First, we present the real-time Coulomb explosion imaging of ultrafast isomerization of C 2D2 2+ by using intense few-cycle laser pulses (&lt
10 fs, ∼1 PW/cm2, ∼800 nm) to show that the hydrogen migration proceeds recurrently in competition with the molecular dissociation. Secondly, we present a new experimental setup for the real-time inner-core excitation imaging, focusing on the generation and separation of the light source using the 59th order harmonic pulses (∼91 eV) and their characteristics. © 2009 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/185/1/012009

Acetylene-vinylidene isomerization in ultrashort intense laser fields studied by triple ion-coincidence momentum imaging Reviewed

Akiyoshi Hishikawa, Akitaka Matsuda, Eiji J. Takahashi, Mizuho Fushitani

JOURNAL OF CHEMICAL PHYSICS Vol. 128 ( 8 ) 2008.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The isomerization of acetylene via hydrogen migration in intense laser fields (8 X 10 14 W/cm(2)) has been investigated by coincidence momentum imaging of the three-body Coulomb explosion process, C(2)H(2)(3+)-> H(+)C(+)CH(+). When ultrashort (9 fs) laser pulses are used, the angle between the momenta of C(+) and H(+) fragments exhibits a sharp distribution peaked at a small angle (similar to 20 degrees), showing that the hydrogen atom remains near the original carbon site in the acetylene configuration. On the other hand, a significantly broad distribution extending to larger momentum angles (similar to 120 degrees) is observed when the pulse duration is increased to 35 fs, indicating that the ultrafast isomerization to vinylidene is induced in the longer laser pulse, (c) 2008 American Institute of Physics.

DOI： 10.1063/1.2828557

Acetylene-vinylidene isomerization in ultrashort intense laser fields studied by triple ion-coincidence momentum imaging Reviewed

Hishikawa, A. and Matsuda, A. and Takahashi, E. J. and Fushitani, M.

Journal of Chemical Physics Vol. 128 ( 8 ) page： 084302 2008

Language：English Publishing type：Research paper (scientific journal)

The isomerization of acetylene via hydrogen migration in intense laser fields (8 X 10 14 W/cm(2)) has been investigated by coincidence momentum imaging of the three-body Coulomb explosion process, C(2)H(2)(3+)-> H(+)C(+)CH(+). When ultrashort (9 fs) laser pulses are used, the angle between the momenta of C(+) and H(+) fragments exhibits a sharp distribution peaked at a small angle (similar to 20 degrees), showing that the hydrogen atom remains near the original carbon site in the acetylene configuration. On the other hand, a significantly broad distribution extending to larger momentum angles (similar to 120 degrees) is observed when the pulse duration is increased to 35 fs, indicating that the ultrafast isomerization to vinylidene is induced in the longer laser pulse, (c) 2008 American Institute of Physics.

DOI： Doi 10.1063/1.2828557

Visualizing recurrently migrating hydrogen in acetylene dication by intense ultrashort laser pulses Reviewed

Akiyoshi Hishikawa, Akitaka Matsuda, Mizuho Fushitani, Eiji J. Takahashi

PHYSICAL REVIEW LETTERS Vol. 99 ( 25 ) 2007.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We demonstrate the visualization of ultrafast hydrogen migration in deuterated acetylene dication (C(2)D(2)(2+)) by employing the pump-probe Coulomb explosion imaging with sub-10-fs intense laser pulses (9 fs, 0.13 PW/cm(2), 800 nm). It is shown, from the temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C(2)D(2)(3+) -> D(+)+C(+)+CD(+), that the migration proceeds in a recurrent manner: The deuterium atom first shifts from one carbon site to the other in a short time scale (similar to 90 fs) and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.

DOI： 10.1103/PhysRevLett.99.258302

Dalitz plot analysis of Coulomb exploding O-3 in ultrashort intense laser fields Reviewed

Akitaka Matsuda, Eiji J. Takahashi, Akiyoshi Hishikawa

JOURNAL OF CHEMICAL PHYSICS Vol. 127 ( 11 ) 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The three-body Coulomb explosion of O-3, O-3(3+)-> O++O++O+, in ultrashort intense laser fields (2x10(15) W/cm(2)) is studied with two different pulse durations (9 and 40 fs) by the coincidence momentum imaging method. In addition to a decrease in the total kinetic energy release, a broadening in the Dalitz plot distribution [Philos. Mag. 44, 1068 (1953)] is observed when the pulse duration is increased from 9 to 40 fs. The analysis based on a simple Coulomb explosion model shows that the geometrical structure of O-3 remains almost unchanged during the interaction with the few-cycle intense laser fields, while a significant structural deformation along all the three vibrational coordinates, including the antisymmetric stretching coordinate, is identified in the 40 fs intense laser fields. The observed nuclear dynamics are discussed in terms of the population transfer to the excited states of O-3. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2766718

Electronic and nuclear responses of fixed-in-space H2S to ultrashort intense laser fields (vol 97, art no 243002, 2006) Reviewed

Akiyoshi Hishikawa, Eiji J. Takahashi, Akitaka Matsuda

PHYSICAL REVIEW LETTERS Vol. 98 ( 1 ) 2007.1

Visualizing recurrently migrating hydrogen in acetylene dication by intense ultrashort laser pulses Reviewed

Hishikawa, A. and Matsuda, A. and Fushitani, M. and Takahashi, E. J.

Physical Review Letters Vol. 99 ( 25 ) page： 258302 2007

Language：English Publishing type：Research paper (scientific journal)

We demonstrate the visualization of ultrafast hydrogen migration in deuterated acetylene dication (C(2)D(2)(2+)) by employing the pump-probe Coulomb explosion imaging with sub-10-fs intense laser pulses (9 fs, 0.13 PW/cm(2), 800 nm). It is shown, from the temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C(2)D(2)(3+) -> D(+)+C(+)+CD(+), that the migration proceeds in a recurrent manner: The deuterium atom first shifts from one carbon site to the other in a short time scale (similar to 90 fs) and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.

DOI： Doi 10.1103/Physrevlett.99.258302

Dalitz plot analysis of Coulomb exploding O-3 in ultrashort intense laser fields Reviewed

Matsuda, A. and Takahashi, E. J. and Hishikawa, A.

Journal of Chemical Physics Vol. 127 ( 11 ) page： 114318 2007

Language：English Publishing type：Research paper (scientific journal)

The three-body Coulomb explosion of O-3, O-3(3+)-> O++O++O+, in ultrashort intense laser fields (2x10(15) W/cm(2)) is studied with two different pulse durations (9 and 40 fs) by the coincidence momentum imaging method. In addition to a decrease in the total kinetic energy release, a broadening in the Dalitz plot distribution [Philos. Mag. 44, 1068 (1953)] is observed when the pulse duration is increased from 9 to 40 fs. The analysis based on a simple Coulomb explosion model shows that the geometrical structure of O-3 remains almost unchanged during the interaction with the few-cycle intense laser fields, while a significant structural deformation along all the three vibrational coordinates, including the antisymmetric stretching coordinate, is identified in the 40 fs intense laser fields. The observed nuclear dynamics are discussed in terms of the population transfer to the excited states of O-3. (c) 2007 American Institute of Physics.

DOI： Doi 10.1063/1.2766718

Coincidence momentum imaging of two- and three-body Coulomb explosion of ethanol in intense laser fields Reviewed

Ryuji Itakura, Takahiro Teramoto, Akiyoshi Hishikawa, Kaoru Yamanouchi

ULTRAFAST OPTICS V Vol. 132 page： 375 - + 2007

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPRINGER

Dissociative ionization of ethanol in intense laser fields is investigated by the coincidence momentum imaging method. Two-body Coulomb explosion channels with the hydrogen migration are identified in addition to a three-body Coulomb explosion channel. On the basis of the momentum vector distributions of the fragment ions, the dissociative ionization dynamics is discussed.

DOI： 10.1007/978-0-387-49119-6_49

Coulomb explosion imaging of molecular dynamics in intense laser fields Reviewed

Akiyoshi Hishikawa, Kaoru Yamanouchi

Springer Series in Chemical Physics Vol. 85 page： 1 - 24 2007

Language：English Publishing type：Research paper (international conference proceedings)

The nuclear dynamics of polyatomic molecules in intense laser fields (∼1 PW/cm2) is studied through the momentum imaging of the fragment ions produced through Coulomb explosion. Characteristic nuclear dynamics that occur on the multidimensional potential energy surfaces in intense laser fields, such as sequential and concerted bond-breaking and hydrogen migration, are elucidated from momentum correlations among the fragment ions. © 2007 Springer-Verlag.

DOI： 10.1007/978-3-540-38156-3-1

Visualizing recurrently migrating hydrogen by few-cycle intense laser pulses Reviewed

Akiyoshi Hishikawa, Akitaka Matsudal, Mizuho Fushitani, Eiji J. Takahashi

XXV INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS Vol. 88 page： 12056 2007

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

Ultrafast hydrogen migration in deuterated acetylene dication (C(2)D(2)(2+)) is studied by the pump-probe Coulomb explosion imaging with few-cycle intense laser pulses (9 fs, 0.13 PW/cm(2), 800 nm). The temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C(2)D(2)(3+) -> D(+) + C(+) + CD(+), shows that the migration proceeds in a recurrent manner: The deuterium atom first shifts from one carbon site to the other in a short time scale (similar to 90 fs), and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.

DOI： 10.1088/1742-6596/88/1/012056

Visualizing recurrently migrating hydrogen by few-cycle intense laser pulses Reviewed

Akiyoshi Hishikawa, Akitaka Matsudal, Mizuho Fushitani, Eiji J. Takahashi

XXV INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS Vol. 88 2007

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

Ultrafast hydrogen migration in deuterated acetylene dication (C(2)D(2)(2+)) is studied by the pump-probe Coulomb explosion imaging with few-cycle intense laser pulses (9 fs, 0.13 PW/cm(2), 800 nm). The temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C(2)D(2)(3+) -> D(+) + C(+) + CD(+), shows that the migration proceeds in a recurrent manner: The deuterium atom first shifts from one carbon site to the other in a short time scale (similar to 90 fs), and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.

DOI： 10.1088/1742-6596/88/1/012056

Electronic and nuclear responses of fixed-in-space H2S to ultrashort intense laser fields Reviewed

Akiyoshi Hishikawa, Eiji J. Takahashi, Akitaka Matsuda

PHYSICAL REVIEW LETTERS Vol. 97 ( 24 ) 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

The Coulomb explosion dynamics of H2S, H2S3+-> H++S++H+, in ultrashort intense laser fields (12 fs, similar to 2x10(14) W/cm(2)) is studied by the coincidence momentum imaging of the three fragment ions. Different electronic and nuclear responses are identified depending on the direction of laser polarization epsilon in the molecular frame. The dependence can be interpreted in terms of the electronic and bonding characters of charge transfer states of H2S coupled to the electronic ground state.

DOI： 10.1103/PhysRevLett.97.243002

Dissociative ATI of H-2 and D-2 in intense soft x-ray laser fields Reviewed

K Hoshina, A Hishikawa, K Kato, T Sako, K Yamanouchi, EJ Takahashi, Y Nabekawa, K Midorikawa

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 39 ( 4 ) page： 813 - 829 2006.2

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The dissociative photoionization processes of H-2 and D-2 in an intense, short-pulsed soft x-ray field (lambda = 29.6 nm, 3 x 10(12) W CM-2, 15 fs) generated as the 27th high-order harmonic of a Ti:sapphire laser is investigated for the first time by time-of-flight mass spectrometry. The ejected H+ fragment ions from H2 are distributed in the kinetic energy range of 3-20 eV peaked at 10.0 eV, and the yield exhibits a nonlinear dependence of the order of 1.7(l) on the light field intensity of the 27th harmonic. Similarly, the D+ fragment ions from D-2 are distributed in the 3-20 eV range peaked at 10.3 eV, and the yield exhibits a nonlinear dependence of the order of 1.6 +/- 0.2. The kinetic energy distributions of H+ and D+ and the nonlinearity in their yields are interpreted well by the two coexisting ionization processes: (i) one-photon dissociative ionization and (ii) dissociative two-photon above-threshold-ionization (ATI) mainly into the repulsive 2p pi(u) state.

DOI： 10.1088/0953-4075/39/4/007

Electronic and nuclear responses of fixed-in-space H2S to ultrashort intense laser fields Reviewed

Hishikawa, A. and Takahashi, E. J. and Matsuda, A.

Physical Review Letters Vol. 97 ( 24 ) page： 243002 2006

Language：English Publishing type：Research paper (scientific journal)

The Coulomb explosion dynamics of H2S, H2S3+-> H++S++H+, in ultrashort intense laser fields (12 fs, similar to 2x10(14) W/cm(2)) is studied by the coincidence momentum imaging of the three fragment ions. Different electronic and nuclear responses are identified depending on the direction of laser polarization epsilon in the molecular frame. The dependence can be interpreted in terms of the electronic and bonding characters of charge transfer states of H2S coupled to the electronic ground state.

DOI： Doi 10.1103/Physrevlett.97.243002

Dissociative ATI of H-2 and D-2 in intense soft x-ray laser fields Reviewed

Hoshina, K. and Hishikawa, A. and Kato, K. and Sako, T. and Yamanouchi, K. and Takahashi, E. J. and Nabekawa, Y. and Midorikawa, K.

Journal of Physics B-Atomic Molecular and Optical Physics Vol. 39 ( 4 ) page： 813-829 2006

Language：English Publishing type：Research paper (scientific journal)

The dissociative photoionization processes of H-2 and D-2 in an intense, short-pulsed soft x-ray field (lambda = 29.6 nm, 3 x 10(12) W CM-2, 15 fs) generated as the 27th high-order harmonic of a Ti:sapphire laser is investigated for the first time by time-of-flight mass spectrometry. The ejected H+ fragment ions from H2 are distributed in the kinetic energy range of 3-20 eV peaked at 10.0 eV, and the yield exhibits a nonlinear dependence of the order of 1.7(l) on the light field intensity of the 27th harmonic. Similarly, the D+ fragment ions from D-2 are distributed in the 3-20 eV range peaked at 10.3 eV, and the yield exhibits a nonlinear dependence of the order of 1.6 +/- 0.2. The kinetic energy distributions of H+ and D+ and the nonlinearity in their yields are interpreted well by the two coexisting ionization processes: (i) one-photon dissociative ionization and (ii) dissociative two-photon above-threshold-ionization (ATI) mainly into the repulsive 2p pi(u) state.

Concerted and sequential Coulomb explosion processes of N2O in intense laser fields by coincidence momentum imaging Reviewed

M Ueyama, H Hasegawa, A Hishikawa, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 123 ( 15 ) 2005.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The Coulomb explosion dynamics of N2O in intense laser fields (800 nm, 60 fs, similar to 0.16 PW/cm(2)) is studied by the coincidence momentum imaging method. From the momentum correlation maps obtained for the three-body fragmentation pathway, N2O3+-> N++N++O+, the ultrafast structural deformation dynamics of N2O prior to the Coulomb explosion is extracted. It is revealed that the internuclear N-N and N-O distances stretch simultaneously as the bond angle > N-N-O decreases. In addition, two curved thin distributions are identified in the momentum correlation maps, and are interpreted well as those originating from the sequential dissociation pathway, N2O3+-> N++NO2+-> N++N++O+. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.2032988

Probing the ultrafast nuclear motion in CS22+ in intense laser fields Reviewed

A Hishikawa, M Ueyama, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 122 ( 15 ) 2005.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The temporal evolution of the nuclear wave packet of CS(2)2+ formed in an intense laser field (60 fs, 0.13 PW/cm(2)) is traced in real time by the pump-and-probe technique combined with coincidence momentum imaging of the Coulomb explosion process, CS23+->S+ + C+ + S+. The momentum correlations among the fragment ions obtained as a function of the pump-probe time delay between 133 fs to 3 ps reveal that the nuclear wave packet in CS22+ evolves not only along the anti-symmetric stretching coordinate to yield S+ and CS+ but also along the symmetric stretching coordinate leading to the simultaneous breaking of the two C-S bonds. The contribution from two different electronic states having bent and linear-type geometrical configurations is identified in the wave packet motion along the bending coordinate of CS22+. 2005 American Institute of Physics.

DOI： 10.1063/1.1895745

Probing the ultrafast nuclear motion in CS22+ in intense laser fields Reviewed

Hishikawa, A. and Ueyama, M. and Yamanouchi, K.

Journal of Chemical Physics Vol. 122 ( 15 ) page： 151104 2005

Language：English Publishing type：Research paper (scientific journal)

The temporal evolution of the nuclear wave packet of CS(2)2+ formed in an intense laser field (60 fs, 0.13 PW/cm(2)) is traced in real time by the pump-and-probe technique combined with coincidence momentum imaging of the Coulomb explosion process, CS23+->S+ + C+ + S+. The momentum correlations among the fragment ions obtained as a function of the pump-probe time delay between 133 fs to 3 ps reveal that the nuclear wave packet in CS22+ evolves not only along the anti-symmetric stretching coordinate to yield S+ and CS+ but also along the symmetric stretching coordinate leading to the simultaneous breaking of the two C-S bonds. The contribution from two different electronic states having bent and linear-type geometrical configurations is identified in the wave packet motion along the bending coordinate of CS22+. 2005 American Institute of Physics.

DOI： Doi 10.1063/1.1895745

Concerted and sequential Coulomb explosion processes of N2O in intense laser fields by coincidence momentum imaging Reviewed

Ueyama, M. and Hasegawa, H. and Hishikawa, A. and Yamanouchi, K.

Journal of Chemical Physics Vol. 123 ( 15 ) page： 154305 2005

Language：English Publishing type：Research paper (scientific journal)

The Coulomb explosion dynamics of N2O in intense laser fields (800 nm, 60 fs, similar to 0.16 PW/cm(2)) is studied by the coincidence momentum imaging method. From the momentum correlation maps obtained for the three-body fragmentation pathway, N2O3+-> N++N++O+, the ultrafast structural deformation dynamics of N2O prior to the Coulomb explosion is extracted. It is revealed that the internuclear N-N and N-O distances stretch simultaneously as the bond angle > N-N-O decreases. In addition, two curved thin distributions are identified in the momentum correlation maps, and are interpreted well as those originating from the sequential dissociation pathway, N2O3+-> N++NO2+-> N++N++O+. (c) 2005 American Institute of Physics.

DOI： Doi 10.1063/1.2032988

Hydrogen migration in acetonitrile in intense laser fields in competition with two-body Coulomb explosion Reviewed

A Hishikawa, H Hasegawa, K Yamanouchi

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 141 ( 2-3 ) page： 195 - 200 2004.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Two-body Coulomb explosion processes of acetonitrile (CH3CN) and deuterated acetonitrile (CD3CN), CH3CN2+ --> CH3-n+ +HnCN+ and CD3CN2+ --> CD3-n+ +DnCN+ (n = 0-2), in an intense laser field (0.15 pW/cm(2), 70 fs) are investigated by the coincidence momentum imaging method. The comparable yields derived for the three pathways (n = 0-2) shows that the hydrogen atom migration proceeds in competition with the Coulomb explosion. The angular distributions of the fragment ions for n = 0 exhibits a sharp peak along the laser polarization direction while the angular distribution becomes more isotropic as n increases. Based on a least-squares analysis of the fragment anisotropy, the dissociation lifetimes of the doubly charged acetonitrile were determined, from which the time scale of the hydrogen migration as well as the deformation of the C-C-N skeleton prior to the explosion were discussed. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2004.06.009

Nuclear dynamics on the light-dressed potential energy surface Of CS2 by coincidence momentum imaging Reviewed

A Hishikawa, H Hasegawa, K Yamanouchi

CHEMICAL PHYSICS LETTERS Vol. 388 ( 1-3 ) page： 1 - 6 2004.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The non-sequential three-body Coulomb explosion, CS23+ --> S+ + C+ + S+, in an intense laser field (0.2 PW/cm(2), 60 fs) is studied by the coincidence momentum imaging of the fragment ions. The observed angular distribution of the momentum vectors of the two S+ ions, p(1) (S+) and p(2)(S+), exhibits a peak at an angle as small as theta(12) similar to 140degrees, showing that the nuclear motion is induced along the bending coordinate to a large extent prior to the explosion. On the other hand, the difference between their absolute values, Deltap(12) = \p(1)(S+)\ - \p(2)(S+), has a sharp distribution peaked at Deltap(12) = 0, suggesting that the symmetric stretching motion dominates over the antisymmetric stretching motion in the laser field. Based on the energy dependence of the momentum vector correlation, the characteristic nuclear dynamics of CS2 on the light-dressed potential energy surfaces in an intense laser field is discussed. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2004.01.128

Hydrogen migration in acetonitrile in intense laser fields in competition with two-body Coulomb explosion Reviewed

Hishikawa, A. and Hasegawa, H. and Yamanouchi, K.

Journal of Electron Spectroscopy and Related Phenomena Vol. 141 ( 2-3 ) page： 195-200 2004

Language：English Publishing type：Research paper (scientific journal)

Two-body Coulomb explosion processes of acetonitrile (CH3CN) and deuterated acetonitrile (CD3CN), CH3CN2+ --> CH3-n+ +HnCN+ and CD3CN2+ --> CD3-n+ +DnCN+ (n = 0-2), in an intense laser field (0.15 pW/cm(2), 70 fs) are investigated by the coincidence momentum imaging method. The comparable yields derived for the three pathways (n = 0-2) shows that the hydrogen atom migration proceeds in competition with the Coulomb explosion. The angular distributions of the fragment ions for n = 0 exhibits a sharp peak along the laser polarization direction while the angular distribution becomes more isotropic as n increases. Based on a least-squares analysis of the fragment anisotropy, the dissociation lifetimes of the doubly charged acetonitrile were determined, from which the time scale of the hydrogen migration as well as the deformation of the C-C-N skeleton prior to the explosion were discussed. (C) 2004 Elsevier B.V. All rights reserved.

Hydrogen migration in acetonitrile in intense laser fields studied by coincidence momentum imaging Reviewed

Hishikawa, A. and Hasegawa, H. and Yamanouchi, K.

Physica Scripta Vol. T110 page： 108-111 2004

Language：English Publishing type：Research paper (scientific journal)

The two-body Coulomb explosion of acetonitrile, CH3CN2+ -> CH3-n+ + HnCN+(n = 0-2), in intense laser fields (0.15 PW/cm(2), 70 fs) is studied by the coincidence momentum imaging technique. It is found that the fragment ions for n 0 are ejected mostly in the direction of the laser polarization vector with < cos(2)theta > = 0.68, where theta is the angle between the fragment recoil direction and the laser polarization vector, while the angle distribution becomes more isotropic as n increases, i.e., < cos(2)theta > = 0.49 for n = 1 and < cos(2)theta > = 0.37 for n = 2. From this characteristic correlation between the anisotropy in the fragment ejection and the hydrogen migration, the Coulomb explosion dynamics competing with the hydrogen atom transfer from the methyl group to the nitrile group is investigated.

Nuclear dynamics on the light-dressed potential energy surface of CS2 by coincidence momentum imaging Reviewed

Hishikawa, A. and Hasegawa, H. and Yamanouchi, K.

Chemical Physics Letters Vol. 388 ( 1-3 ) page： 1-6 2004

Language：English Publishing type：Research paper (scientific journal)

The non-sequential three-body Coulomb explosion, CS23+ --> S+ + C+ + S+, in an intense laser field (0.2 PW/cm(2), 60 fs) is studied by the coincidence momentum imaging of the fragment ions. The observed angular distribution of the momentum vectors of the two S+ ions, p(1) (S+) and p(2)(S+), exhibits a peak at an angle as small as theta(12) similar to 140degrees, showing that the nuclear motion is induced along the bending coordinate to a large extent prior to the explosion. On the other hand, the difference between their absolute values, Deltap(12) = \p(1)(S+)\ - \p(2)(S+), has a sharp distribution peaked at Deltap(12) = 0, suggesting that the symmetric stretching motion dominates over the antisymmetric stretching motion in the laser field. Based on the energy dependence of the momentum vector correlation, the characteristic nuclear dynamics of CS2 on the light-dressed potential energy surfaces in an intense laser field is discussed. (C) 2004 Elsevier B.V. All rights reserved.

Hydrogen migration in acetonitrile in intense laser fields studied by coincidence momentum imaging Reviewed

Akiyoshi Hishikawa, Hirokazu Hasegawa, Kaoru Yamanouchi

PHYSICA SCRIPTA Vol. T110 page： 108 - 111 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The two-body Coulomb explosion of acetonitrile, CH3CN2+ -> CH3-n+ + HnCN+(n = 0-2), in intense laser fields (0.15 PW/cm(2), 70 fs) is studied by the coincidence momentum imaging technique. It is found that the fragment ions for n 0 are ejected mostly in the direction of the laser polarization vector with < cos(2)theta > = 0.68, where theta is the angle between the fragment recoil direction and the laser polarization vector, while the angle distribution becomes more isotropic as n increases, i.e., < cos(2)theta > = 0.49 for n = 1 and < cos(2)theta > = 0.37 for n = 2. From this characteristic correlation between the anisotropy in the fragment ejection and the hydrogen migration, the Coulomb explosion dynamics competing with the hydrogen atom transfer from the methyl group to the nitrile group is investigated.

DOI： 10.1238/Physica.Topical.110a00108

Hydrogen migration in acetonitrile in intense laser fields studied by coincidence momentum imaging Reviewed

Akiyoshi Hishikawa, Hirokazu Hasegawa, Kaoru Yamanouchi

Physica Scripta T Vol. T110 page： 108 - 111 2004

Language：English Publishing type：Research paper (scientific journal)

The two-body Coulomb explosion of acetonitrile, CH3CN 2+ → CH3-n+ + HnCN+ (n = 0-2), in intense laser fields (0.15 PW/cm2, 70 fs) is studied by the coincidence momentum imaging technique. It is found that the fragment ions for n = 0 are ejected mostly in the direction of the laser polarization vector with 〈 cos2 θ 〉 = 0.68, where θ is the angle between the fragment recoil direction and the laser polarization vector, while the angle distribution becomes more isotropic as n increases, i.e., 〈 cos2 θ 〉 = 0.49 for n = 1 and 〈 cos2 θ 〉 = 0.37 for n = 2. From this characteristic correlation between the anisotropy in the fragment ejection and the hydrogen migration, the Coulomb explosion dynamics competing with the hydrogen atom transfer from the methyl group to the nitrile group is investigated. © Physica Scripta 2004.

DOI： 10.1238/Physica.Topical.110a00108

Sequential three-body Coulomb explosion of CS2 in intense laser fields appearing in momentum correlation map Reviewed

A Hishikawa, H Hasegawa, K Yamanouchi

CHEMICAL PHYSICS LETTERS Vol. 361 ( 3-4 ) page： 245 - 250 2002.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The three-body Coulomb explosion process of CS2 in intense laser fields (60 fs, 0.36 x 10(15) W/cm(2)), CS23+ --> S+ + C+ + S+, is studied by the triple coincidence momentum imaging of the atomic fragment ions. The set of the observed momentum vectors of the fragment ions determined for respective explosion events exhibits a clear trajectory originating from the rotational motion of an intermediate CS2+ ion, formed in a sequential explosion process of CS23+ prior to the complete three-body fragmentation. The contribution of the sequential pathway to the overall three-body explosion process is estimated to be 17(1)%. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(02)00880-1

Suppression of decomposition of aniline cation in intense laser fields by cluster formation with ammonia molecules Reviewed

J Watanabe, R Itakura, A Hishikawa, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 116 ( 22 ) page： 9697 - 9702 2002.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Mass-selected aniline cations and [aniline-(NH3)(n)](+) (n=1 and 2) cluster ions are exposed to the femtosecond laser fields (lambdasimilar to395 nm,Isimilar to4x10(15) W/cm(2)) and the nanosecond laser fields (lambda=532 nm,Isimilar to2.7x10(10) W/cm(2)) by using a tandem type time-of-flight mass spectrometer. In the case of the bare aniline cation, the decomposition forming the five-membered ring compound, cyclopentadienyl cation (C5H6+), dominantly proceeds in both the femtosecond and nanosecond laser fields. When one or two ammonia molecules are attached to the aniline cation, the decomposition is significantly suppressed. This suppression was interpreted in terms of an intermolecular energy flow through the hydrogen bonding. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1475753

Coincidence Imaging of coulomb explosion of CS2 in intense laser fields Reviewed

H Hasegawa, K Doi, A Hishikawa, K Yamanouchi

SCIENCE OF SUPERSTRONG FIELD INTERACTIONS Vol. 634 page： 197 - 198 2002

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The coincidence imaging technique is applied to direct determination of the momentum vectors of all the fragment ions produced through every event of the Coulomb explosion of a single molecular ion, CS2+ (z = 2 - 4) formed in intense laser fields (0.36 PW/cm(2)). The molecular structure Of CS23+ just before the three-body Coulomb explosion is reconstructed from the measured momentum vectors of the atomic fragment ions. It was confirmed that the skeletal deformation of CS2 is induced to a large extent in intense laser fields.

Coincidence imaging of Coulomb explosion of CS2 in intense laser fields Reviewed

H Hasegawa, A Hishikawa, K Yamanouchi

CHEMICAL PHYSICS LETTERS Vol. 349 ( 1-2 ) page： 57 - 63 2001.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The coincidence imaging technique is applied to direct determination of the momentum vectors of all the fragment ions produced through every event of the Coulomb explosion of a single molecular ion, CS22+ (z = 2-4) formed in intense laser of CS23+ just fields (similar to 60 fs, 0.36 x 10(15) W/cm(2)). The molecular structure I before the Coulomb explosion, CS23+ --> S+ + C+ + S+, is reconstructed from the measured momentum vectors of the fragment ions. The mean C-S bond length of <r > = 2.5 Angstrom and the azimuthally averaged S-C-S bond angle, < gamma > = 145 degrees, thus determined indicate that structural deformation occurs to a large extent in the intense laser fields. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(01)01087-9

Real-time probing of alignment and structural deformation of CS2 in intense nanosecond laser fields Reviewed

A Iwasaki, A Hishikawa, K Yamanouchi

CHEMICAL PHYSICS LETTERS Vol. 346 ( 5-6 ) page： 379 - 386 2001.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

A time evolution of the alignment and structural deformation processes of neutral CS2 in intense non-resonant nanosecond laser fields (1.9 X 10(12) W/cm(2)) is derived by ionizing CS2 using intense circularly polarized feintosecond laser fields (5.5 x 10(14) W/cm(2)). From the real-time probing of the momentum distribution of the resultant S3+ and C2+ fragment ions produced through the Coulomb explosion induced by the intense fenitosecond laser fields, it is identified that the alignment and the structural deformation proceed simultaneously in the nanosecond laser fields. (C) 2001 Elsevier Science BN. All rights reserved.

DOI： 10.1016/S0009-2614(01)00963-0

Light-induced multiple electronic-state coupling of O-2(+) in intense laser fields Reviewed

A Hishikawa, SL Liu, A Iwasaki, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 114 ( 22 ) page： 9856 - 9862 2001.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The dissociation processes, O-2(+)-->O++O, in intense laser fields (100 fs, similar to 3x10(14) W/cm(2)) are studied at the laser wavelength of 795 and 398 nm on the basis of the momentum imaging maps of the O+ fragment ions. The covariance map measurements are performed with high momentum resolution to assign securely the dissociation pathways. From the anisotropic momentum distribution of O+ with respect to the laser polarization direction, the electronic states of O-2(+) are found to be coupled exclusively through parallel transitions in the course of the dissociation process. The released kinetic energy of O+ for both 795 and 398 nm are interpreted consistently by a sequential coupling model of light-dressed potential curves of O-2(+) in the quartet Pi state manifold. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1368383

Ionization and fragmentation dynamics of benzene in intense laser fields by tandem mass spectroscopy Reviewed

R Itakura, J Watanabe, A Hishikawa, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 114 ( 13 ) page： 5598 - 5606 2001.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Using a tandem time-of-flight mass spectrometer, benzene cations produced by the resonantly enhanced multiphoton ionization are mass separated and are exposed to intense laser fields (similar to 2x10(16) W/cm(2)) at lambda similar to 790 and 395 nm with the pulse duration of similar to 50 fs. Comparing the yields of the product ions with those obtained from neutral benzene molecules, the ionization and dissociation dynamics of benzene in intense laser fields is investigated. At lambda similar to 790 nm, the formation of parent benzene ions is a dominant process irrespective of the initial charge states, i.e., major products obtained when starting from neutral benzene are benzene cations and dications and those obtained when starting from benzene cation are benzene dications. On the other hand, at lambda similar to 395 nm, the fragmentation processes to produce C4Hi+(i=2-4) and C3Hj+(j=1-3) dominate over further ionization to the benzene dication for both cases starting from neutral benzene and benzene cation, indicating the population trapping occurs by the efficient confinement in the light-dressed mixture of the C and X states of benzene cations assisted by the ultrafast intramolecular decay process. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1352619

Resonance-state selective photodissociation of OCS (2(1)Sigma(+)): Rotational and vibrational distributions of CO fragments Reviewed

R Itakura, A Hishikawa, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 113 ( 16 ) page： 6598 - 6607 2000.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The rotational and vibrational state distributions of the CO fragments produced through the photodissociation of OCS in the vacuum ultraviolet (VUV) region (150-155 nm), OCS (2 (1)Sigma (+))--> CO (X (1)Sigma (+))+S(S-1), are derived for the three lowest quasi-bound vibrational resonances (upsilon*=0-2) in the 2 (1)Sigma (+) state. The rotational state distributions of the CO fragments in the upsilon (CO)=0 and 1 vibrational states are determined, respectively, by the analysis of the rotational structures in the laser-induced fluorescence (LIF) spectra of the A(1)Pi -X (1)Sigma (+)(0,0) and (1,1) transitions of CO. The rotational temperatures of CO in the upsilon (CO)=0 state are low (similar to 100 K) for all the three resonances, while those in the upsilon (CO)=1 state are substantially higher, i.e., 2210, 940, and 810 K for upsilon*=0, 1, and 2, respectively. The vibrational state distributions of CO are derived from the Doppler spectroscopy of the counterpart S(S-1) fragments. From the analysis of the observed Doppler profiles, it is found for all the three lowest vibrational resonances of OCS that the vibrational distributions are represented well by the Boltzmann-type distribution with a vibrational temperature of around 7000 K. On the basis of these new findings, the energy partitioning in the photodissociation process through these three vibrational resonances in the 2 (1)Sigma (+) state is discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)01740-2].

DOI： 10.1063/1.1310606

Extraction of molecular dynamics in intense laser fields from mass-resolved momentum imaging maps: application to Coulomb explosion of NO Reviewed

A Iwamae, A Hishikawa, K Yamanouchi

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 33 ( 2 ) page： 223 - 240 2000.1

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The nuclear dynamics of NO in intense laser fields (similar to 1.4 PW cm(-2)) is studied on the basis of the momentum-scaled time-of-flight spectra and mass-resolved momentum imaging maps of the atomic fragment ions, NP+ and Oq+ (p, q = 1-3), produced from the (p, q) Coulomb explosion pathways of NO, i.e. NO(p+q)+ --> Np+ + Oq+. A procedure to extract nuclear dynamics from the momentum maps is proposed by taking account of the effect of the finite detector size. The resultant nine (p, q) single-pathway components show that (a) the distributions of the N-O internuclear distance of NOz+ just before the Coulomb explosion exhibit significant broadening (similar to 1 Angstrom); (b) the distance at which the corresponding distribution takes a maximum increases from 1.68 to 2.34 Angstrom as z from 2 to 6 with a small amount of suppression at odd z (z = 3, 5); and (c) the atomic fragment ions exhibit narrower angular distributions for a larger total charge z (= p + q) of NOz+.

DOI： 10.1088/0953-4075/33/2/308

Ultrafast structural deformation of polyatomic molecules in intense laser fields Reviewed

K Yamanouchi, A Hishikawa, A Iwamae, SL Liu

PHYSICS OF ELECTRONIC AND ATOMIC COLLISIONS Vol. 500 page： 182 - 191 2000

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The momentum vector distributions of fragment ions produced through the Coulomb explosion of small molecules such as NO, CO2, NO2, and H2O in intense laser fields (similar to 1 PW/cm(2)) are measured by the mass-resolved momentum imaging (MRMI) technique. For NO, the MRMI maps for a single (p,q) pathway, NO(p+q)+ --> NP+ + Oq+ (p, q = 1 similar to 3), are extracted from the observed MRMI maps on the basis of the momentum matching of the NP+ and Oq+. ion pair. In the MRMI maps for the fragment ions produced from CO2, NO2, and H2O, their ultrafast structural deformation both along the stretching coordinate and along the bending coordinate is identified. The <O-C-O angle distribution of CO2 Spreads significantly (FWHM similar to 40 degrees), and the <O-N-O bond angle of NO2 increases toward a linear configuration within the ultrashort duration of the laser pulse. This type of deformation is also identified for H2O. These structural deformations are most reasonably interpreted as a consequence of the formation of light-dressed potential energy surfaces.

Ultrafast structural deformation of NO2 in intense laser fields studied by mass-resolved momentum imaging Reviewed

A Hishikawa, A Iwamae, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 111 ( 19 ) page： 8871 - 8878 1999.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The ultrafast structural deformation of NO2 in an intense laser field (1.0 PW/cm(2)) is studied by mass-resolved momentum imaging (MRMI) of the Op+ and Nq+ (p,q=1-3) fragment ions produced from NO2z+ through the Coulomb explosion processes, NO2z+--> Op++Nq++Or+ (z=p+q+r). The N-O distance just before the Coulomb explosion is elongated significantly from that in the electronic ground state, and it monotonically increases from 1.7 to 2.1 Angstrom as z increases from 4 to 9. The angle O-N-O bond angle increases toward a linear configuration as a function of z, which is interpreted in terms of the formation of the light-dressed potential energy surfaces. The two-body fragmentation pathways to produce NO+ and NO2+ are also investigated by the MRMI measurements to derive the extent of the asymmetrical bond elongation of one of the two N-O bonds. (C) 1999 American Institute of Physics. [S0021-9606(99)00443-2].

DOI： 10.1063/1.480233

Ultrafast deformation of the geometrical structure of CO2 induced in intense laser fields Reviewed

A Hishikawa, A Iwamae, K Yamanouchi

PHYSICAL REVIEW LETTERS Vol. 83 ( 6 ) page： 1127 - 1130 1999.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

Ultrafast deformation of geometrical structure of CO2 in an intense laser field (1.1 PW/cm(2) = 1.1 X 10(15) W/cm(2)) was investigated by momentum imaging of the fragment Op+ and Cq+ (p, q = 1-3) ions produced from CO2z+ through the Coulonnb explosion processes, CO2z+ --> Op+ + Cq+ + Or+ (z = p + q + r). The observed large mean amplitude along the angle O-C-O bond angle (similar to 40 degrees) was attributed to the ultrafast bending motion induced on the light-dressed potential energy surfaces.

DOI： 10.1103/PhysRevLett.83.1127

Vibrational propensity in the predissociation rate of SO2((C)over-tilde(1)B(2)) by two types of nodal patterns in vibrational wavefunctions Reviewed

T Sako, A Hishikawa, K Yamanouchi

CHEMICAL PHYSICS LETTERS Vol. 294 ( 6 ) page： 571 - 578 1998.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The absorption and laser-induced fluorescence spectra of the (C)over-tilde(1)B(2)-(X)over-tilde(1)A(1), band of SO2 were simultaneously measured between 221.5 and 208 nm under jet-cooled conditions. The fluorescence quantum yields above the dissociation threshold showed irregularity, reflecting a level specificity in the predissociation rate. The vibronic-level dependence in the predissociation rate was interpreted in terms of the nodal structure of the vibrational wavefunctions, constructed from a least-squares analysis of the observed vibrational energies in the C state. The vibrational wavefunctions can be categorized into two types of localized wavefunctions: one stretching along the dissociation coordinate which tends to afford a much faster dissociation rate than the other which folds perpendicularly to the dissociation coordinate. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0009-2614(98)00922-1

Coulomb explosion dynamics of N-2 in intense laser field by mass-resolved momentum imaging Reviewed

A Hishikawa, A Iwamae, K Hoshina, M Kono, K Yamanouchi

CHEMICAL PHYSICS Vol. 231 ( 2-3 ) page： 315 - 329 1998.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The Coulomb explosion reactions of N-2, N-2((p+q)+) --> Np+ + Nq+ caused by the irradiation of intense laser light (0.73-6.9 PW/cm(2)) were investigated by high-resolution time-of-flight (TOF) mass spectroscopy and by the mass-resolved two-dimensional momentum imaging (MRMI) method. Six explosion pathways(p, q) = (1, 1), (1,2), (1,3), (2, 2), (2, 3) and (3, 3) in addition to (0, 1), (0,2) dissociation pathways were identified, whose assignments were securely performed both from the momentum matching between the fragment pair and their correlation with the laser-field intensity dependence. The MRMI method, which visualizes the radial and angular momentum distributions of mass-selected fragment ions on a two-dimensional momentum plane, was used to correlate ion fragments produced after the Coulomb explosion. By examining theoretically synthesized MRMI maps, it was found that the momentum distributions of the fragment ions in a wide momentum range can be extracted by the MRMI technique. The relative yields of the explosion pathways at six different laser-field intensities were evaluated from the three-dimensional integration of the MRMI maps, and the intensity dependence of the formation of singly and multiply charged parent N-2((p+q) +) ions prior to the fragmentation was derived. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0301-0104(98)00025-1

Omega-type doubling reversal in the B-3 Pi(1) state of (HgAr)-Hg-200 as a probe of the long-range potential of the A(3)Pi(0)+ state Reviewed

A Hishikawa, H Sato, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 108 ( 22 ) page： 9202 - 9205 1998.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The mass-resolved excitation spectrum of the B (II1)-I-3-X(1)Sigma(+) transition of HgAr was measured by the two-color resonantly enhanced two-photon ionization method using a high-resolution reflectron time-of-flight mass spectrometer. The rotational structures were recorded with high spectral resolution (similar to 0.05 cm(-1))for the (upsilon(B),0) bands (upsilon(B) = 0 - 9) of a single isotopomer (HgAr)-Hg-200. From the rotational analysis, the presence of an Omega-type doubling was identified for the first time, which is caused by the rotational perturbation from the nearby highly excited vibrational levels of the A (II0+)-I-3 state. The spacing between the Omega-type doublers was found to exhibit a characteristic reversal as a function of upsilon(B). From the deperturbation of the Omega-type doubling, the vibrational level energies of the A state in the vibrationally highly excited region were derived, from which its long-range interaction potential was determined. (C) 1998 American Institute of Physics. [S0021-9606(98)02822-0].

DOI： 10.1063/1.476415

Mass-resolved VUV laser spectroscopy of XeAr: Two competing predissociation pathways in the C1 state Reviewed

SL Liu, A Hishikawa, K Yamanouchi

JOURNAL OF CHEMICAL PHYSICS Vol. 108 ( 13 ) page： 5330 - 5337 1998.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Mass-resolved excitation spectra of the C1-X0(+) band of XeAr were measured under jet-cooled conditions using a tunable coherent vacuum ultraviolet (VUV) light (lambda similar to 130 nm) as an excitation light source and a high-resolution (m/Delta m similar to 1100) reflectron time-of-flight mass spectrometer. The rotational structure of the C1-X0(+) (upsilon',0) (upsilon'=2-6) vibronic bands were recorded by monitoring the parent (XeAr+)-Xe-132-Ar-40 ions and the fragment Xe-132(+) ions. From the analysis of the rotational structures, the existence of the two dissociation pathways from the C1 state was identified for the first time; i.e., (i) the rotationally dependent predissociation caused by an electron-rotation interaction (L- and/or S-uncoupling) with the dissociative state with 0(-) symmetry correlating with the Xe 6s'(1/2)(0) level, and (ii) the rotationally independent predissociation caused by the electrostatic interaction with a repulsive state with Omega = 1 symmetry correlated either with the Xe 6s(3/2)(1) level or the Xe 6s(3/2)(2) level. From the least-squares fit to the partially resolved rotational structures, the dissociation rates for these two pathways as well as the band origins and the rotational constants, were derived for the upsilon'=2-6 levels in the C1 state. (C) 1998 American Institute of Physics. [S0021-9606(98)01513-X].

DOI： 10.1063/1.475968

Rotational predissociation dynamics of H2O ((C)over-tilde(1)B(1)) by VUV laser-induced photofragment fluorescence spectroscopy Reviewed

SL Liu, A Hishikawa, K Yamanouchi

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 71 ( 2 ) page： 355 - 362 1998.2

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

The rotational predissociation of water molecules in the vibrationless level of the (C) over tilde B-1(1) state was investigated under jet-cooled conditions (27-154 K) by exciting them with a tunable VUV laser in the wavelength range of 124.3-123.7 nm and by detecting the total fluorescence from electronically excited photofragments OH(A(2)Sigma (+)). Due to the simple one-photon selection rule and the efficient rotational cooling, individual low-J rotational transitions of the (C) over tilde B-1(1)-(X) over tilde (1)A(1) origin band were observed with almost no overlap in the laser-induced photofragment fluorescence (LIPF) spectrum. The widths and intensities of these rotational transitions exhibited pronounced dependence on the parent rotational levels in the (C) over tilde B-1(1) state. The least-squares analysis of the observed line-widths (FWHM) of the resolved rotational transitions, Gamma 's, showed that they are well described by the formula, Gamma = Gamma (0) + a(a)[J(a)'(2)], with optimized parameters Gamma (0) = 2.5(1) cm(-1) and a(a) = 0.63(1) cm(-1), indicating that (i) the homogeneous interaction couples the (C) over tilde B-1(1) state with the (A) over tilde B-1(1) state to form OH fragments in the electronically ground (2)Pi (i) state and (ii) the heterogeneous (a-axis orbital-rotation) interaction couples the (C) over tilde B-1(1) state with the (B) over tilde (1)A(1) state to form OH fragments in the electronically excited A(2)Sigma (+) state. By taking account of the rotational line-broadening effect, the least-squares analysis was also performed to fit the observed spectral intensities to derive the branching ratio of the OH(A(2)Sigma (+)) formation via the (B) over tilde (1)A(1) state of H2O. It was found that the OH(A(2)Sigma (+)) formation branching ratio can be expressed by an exponential form, exp(-gamma [J(a)'(2)]), which was proposed first by Hodgson et al. [Mol. Phys., 54, 351 (1985)], and reproduces well the observed rotational intensity pattern when gamma = 0.097(7). By using this branching ratio and the previous data for the absorption oscillator strength, the absolute cross section to yield OH(A(2)Sigma (+)) photofragments was obtained as a function of the excitation energy.

DOI： 10.1246/bcsj.71.355

Cross section for disalignment of excited neon atoms due to neon or helium atom collisions Reviewed

T Wakabayashi, A Yamamoto, T Yaneda, T Furutani, A Hishikawa, T Fujimoto

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 31 ( 2 ) page： 341 - 359 1998.1

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

In a positive column plasma of glow discharge in neon the population of metastable atoms (2p(5)3s configuration) is substantial. Linearly polarized pulsed laser light excited these atoms to one of the 2p(5)3p configuration levels, and the direct fluorescence was observed with its polarized components resolved. From the temporal development of the intensities of these components, the disalignment (depolarization) rate due to atom (neon or helium) collisions was determined. From its atom-density (<3 x 10(23) m(-3)) dependence the rate coefficient was determined, and from the temperature (42-650 K) dependence of the rate coefficient, the disalignment collision cross section was estimated as a function of energy in the energy range of the order of 10 meV. The cross section of the 2p(2) (Paschen notation) atoms has positive dependence on energy, while that of the 2p(7) atoms has a negative dependence. The cross sections thus determined serve asa quantitative test of the molecular potentials to the order of 1 cm(-1).
In order to confirm that the temperature of the metastable atoms in the plasma is equal to the temperature of the surrounding wall, an additional experiment was performed; the line profile of the CW laser-induced fluorescence was observed for a plasma at liquid nitrogen temperature, and the metastable atom temperature was found to be 78 K.

DOI： 10.1088/0953-4075/31/2/015

Mass-resolved two-dimensional momentum imaging of the Coulomb explosion of N-2 and SO2 in an intense laser field Reviewed

A Hishikawa, A Iwamae, K Hoshina, M Kono, K Yamanouchi

CHEMICAL PHYSICS LETTERS Vol. 282 ( 3-4 ) page： 283 - 291 1998.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The Coulomb explosion reactions of N-2 and SO2 caused by the irradiation of intense laser light were investigated by high-resolution mass spectroscopy. For N-2, from the least-squares fit to the split mass patterns for the N+, N2+ and N3+ channels, kinetic energy releases of six explosion pathways were determined. By rotating the laser polarization direction with respect to the detection axis, angular distributions for the singly and multiply charged atomic ion fragments were obtained and were converted to mass-resolved two-dimensional momentum imaging (MRMI) maps. This MRMI method was found to be useful to correlate ion fragments produced after the Coulomb explosion. MRMI was also applied to the Coulomb explosion of SO2. (C) 1998 Elsevier Science B.V.

DOI： 10.1016/S0009-2614(97)01325-0

Coulomb explosion dynamics of N2O in intense laser-field: Identification of new two-body and three-body fragmentation pathways Reviewed

A Hishikawa, A Iwamae, K Hoshina, M Kono, K Yamanouchi

RESEARCH ON CHEMICAL INTERMEDIATES Vol. 24 ( 7 ) page： 765 - 784 1998

Language：English Publisher：VSP BV

The Coulomb explosion process of N2O in an intense laser-field (similar to 5 PW/cm(2)) has been investigated by the high-resolution time-of-flight (TOF) spectroscopy. Six two-body explosion pathways involving the NO+, NO2+, N-2(+) molecular ions have been securely identified from the momentum-scaled TOF spectra of the fragment ions. Assuming a linear geometry, three-body explosion pathways were investigated by sequential and concerted explosion models, When the concerted model is adopted, the observed momentum distributions of six atomic ion channels; N+, N2+, N3+, O+, O2+ and O3+, were well fitted using the Gaussian momentum distribution with the optimized bond elongation factor of 2.2(3). From the yields of individual Coulomb explosion pathways determined by the fit, the abundance of the parent ions, N2Oz+ (z = 2-8), prior to the two- body and three-body explosion processes was found to have a smooth distribution with a maximum at z similar to 3.

DOI： 10.1163/156856798x00401

Experimental and theoretical exploration of photodissociation of SO2 via the (C)over-tilde(1)B(2) state: identification of the dissociation pathway Reviewed

H Katagiri, T Sako, A Hishikawa, T Yazaki, K Onda, K Yamanouchi, K Yoshino

JOURNAL OF MOLECULAR STRUCTURE Vol. 413 page： 589 - 614 1997.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The photodissociation reaction of SO2 via the (C) over tilde(1)B(2) state, SO2 ((C) over tilde(1)B(2)) --> SO((3) Sigma(-)) + O(P-3) was investigated by experimental and theoretical approaches cooperatively to clarify its dissociation mechanism. We measured the laser induced fluorescence (LIF) spectrum of the (C) over tilde-(X) over tilde band in the short UV wavelength region (210-200 nm) under jet-cooled conditions. The fluorescence quantum yields and the dissociation rates of individual vibronic levels were determined in the 220-200-nm region using (i) the LIF spectrum measured in the present study, (ii) that measured previously by Yamanouchi et al. (J. Mol. Struct, 352/353 (1995) 541) in the longer wavelength region above 210 nm, and (iii) the high-resolution absorption spectrum measured by Freeman et al. (Planet. Space. Sci. 32 (1984) 1125). The dissociation rates were also derived in the 210-200-nm region from the broadening of the rotational lines of the (C) over tilde-(X) over tilde vibronic transitions. It was found that the dissociation rates determined through two different procedures were consistent with each other, and that the rate increases almost exponentially as an excess energy above the dissociation threshold increases though there is a certain fluctuation of the dissociation rates reflecting a mode specificity. We also performed theoretical ab initio calculations to derive potential energy surfaces (PESs) of the electronic ground states and low-lying electronically excited states of SO2 within the MCSCF and MRCI levels. The theoretical calculations showed that (i) the PES of the 2(1)A' state (the (C) over tilde(1)B(2) state in C-2r symmetry), correlating with the SO((1) Delta) + O(D-1) asymptote, crosses with the repulsive singlet (3(1)A') state, correlating with the SO((3) Sigma(-)) + O(P-3) asymptote, to form a pseudo-seam, (ii) the crossing pseudo-seam of these two PESs is located near the equilibrium bent angles for the X and C states along the energy contour of similar to 9700 cm(-1) measured from the SO((3) Sigma(-)) + O(P-3) dissociation limit, and (iii) the crossing seam between the 2(1)A' ((C) over tilde(1)B(2)) and repulsive 2(3)A' states is located in a lower energy region than the singlet seam; at similar to 6700 cm(-1) measured from the SO((3) Sigma(-)) + O(P-3) dissociation limit. On the basis of the above experimental and theoretical results together with the previous experimental evidence, we propose that (i) the photodissociation reaction via the (C) over tilde state proceeds mainly through the vibronic mixing between the (C) over tilde state vibronic levels with the quasi-bound dissociation continuum of the electronic ground X(1)A(1) state, and (ii) the additional dissociation channels may be open through the crossing seam with the repulsive singlet (3(1)A') state and that with the repulsive tiplet (2(3)A') slate in their narrow crossing energy regions. (C) 1997 Elsevier Science B.V.

DOI： 10.1016/S0022-2860(97)00199-3

PHOFEX spectroscopy of HgNe and HgAr: Determination of the dissociation energies of the X-1 Sigma(+), A(3)II(0)+, and (BII1)-I-3 states Reviewed

T Tasaka, K Onda, A Hishikawa, K Yamanouchi

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 70 ( 5 ) page： 1039 - 1045 1997.5

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

Photofragment excitation (PHOFEX) spectroscopy was applied to determine the dissociation energies of the B-3 Pi(1) states of HgAr and HgNe. The PHOFEX spectra were measured in the wavelength region where the laser-induced fluorescence spectrum of the B-3 Pi(1)-X-1 Sigma(+) transition exhibits a continuum structure by probing the photolysis product of Hg(6(3)P(1)) through the Hg(8(3)S(1)-6(3)P(1)) transition. By the spectral simulation of the threshold behavior of the high-resolution (Delta v approximate to 0.08 cm(-1)) PHOFEX spectrum, the thresholds for the photodissociation reaction, HgRg --> Hg(6(3)P(1)) + Rg, were determined to be 39447.9(3) and 39536.0(5) cm(-1) for Rg = Ne and Ar, respectively. From these thresholds, the dissociation energies, D-0's, of the B-3 Pi(1) states of HgNe and HgAr were determined to be D-0(B-3 Pi(1); HgNe)= 9.8(3) and Do(B-3 pi(1); HgAr)= 61.8(5) cm(-1), respectively. This direct determination of the dissociation energies of the B-3 Pi(1) states led to a determination of the D-0's for the X-1 Sigma(+) and A(3) Pi(0+) states; D-0(X-1 Sigma(+); HgNe)= 35.6(3), D-0(X-1 Sigma(+); HgAr)= 123.7(5), D-0(A(3) Pi(0+); HgNe)= 68.7(3), and D-0(A(3) Pi(0+); HgAr)= 348.8(6) cm(-1) In addition, the (v',0) vibronic bands of the B-3 Pi(1)-X-1 Sigma(+) transition of HgAr were re-measured with high resolution for v' = 0-8. From the transition wavenumbers of these vibronic bands, the Morse potential parameters were determined with high precision as omega(e) = 11.94(3) cm(-1) and omega(e)x(e) = 0.594(3) cm(-1).

DOI： 10.1246/bcsj.70.1039

Radiative lifetime measurements of the B (2)Sigma(+) state of BaH by laser spectroscopy Reviewed

LE Berg, K Ekvall, A Hishikawa, S Kelly

PHYSICA SCRIPTA Vol. 55 ( 3 ) page： 269 - 272 1997.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SWEDISH ACAD SCIENCES

By applying laser resonance methods in the near infrared wavelength region around 900 nm, a time-resolved experiment has been performed on the low lying B (2) Sigma(+) state of barium hydride. The radiative lifetime is shown to vary with the rotational quantum number due to perturbations between the low lying A' 2 Delta, A (2) Pi and B (2) Sigma(+) states. The following lifetime was obtained for the BaH molecule, where local perturbations are assumed to be negligible:
tau(B (2) Sigma(+)(upsilon' = 0, J = 5.5))= 125 +/- 2ns.

DOI： 10.1088/0031-8949/55/3/003

Femtosecond transition-state dynamics of dissociating OCS on the excited (1)Sigma(+) potential energy surface Reviewed

A Hishikawa, K Ohde, R Itakura, SL Liu, K Yamanouchi, K Yamashita

JOURNAL OF PHYSICAL CHEMISTRY A Vol. 101 ( 4 ) page： 694 - 704 1997.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Ultrafast photodissociation dynamics of OCS on the dissociative potential energy surface (PES) of the electronically excited (1) Sigma(+) state was investigated by photofragment excitation (PHOFEX) spectroscopy and time-dependent wavepacket calculations. The high-resolution PHOFEX spectrum of the entire (1) Sigma(+)-(1) Sigma(+) transition (63 300-69 350 cm(-1)) in the vacuum ultraviolet (vacuum UV) region was measured under jet-cooled conditions by using a tunable vacuum UV laser as an excitation light source and by monitoring the fragment S(S-1) atom. Due to sufficient vibrational and rotational cooling in a supersonic jet, a simple and distinct vibrational progression of the (1) Sigma(+)-(1) Sigma(+) band was recorded free from vibrational hot bands and the broadening by rotational structure. The autocorrelation function obtained from a Fourier transform of the PHOFEX spectra clearly exhibited recurrences with a period of 42 fs, corresponding to a period of the vibrational motion at the transition state along the direction perpendicular to the dissociation coordinate, This interpretation of the ultrafast motion in the transition-state region was supported by the wavepacket calculation on the ab initio PES obtained in the present study, which afforded a period of 48 fs for vibrational motion along the in-phase CO and CS stretching mode at the transition state on the ab initio PES. The distinct six peaks broadened due to the fast dissociation process were assigned to the transitions at the upsilon(TS) 0-5 levels, where upsilon(TS) represents a vibrational quantum number for the Feshbach resonances in the in-phase stretching mode at the transition state. For the upsilon(TS) = 0 peak, the narrowest width corresponding to the lifetime, tau(upsilon(TS)), of tau(0) = 133 fs was obtained. It was found that the dissociation lifetime first becomes shorter for a larger upsilon(TS), i.e., tau(1) = 44 fs and tau(2) = 27 fs, and then, the peak width becomes narrower for the higher vibrational states above upsilon(TS) = 2, with corresponding lifetimes of tau(3) = 47 fs and tau(4) = 44 fs. This deceleration of the dissociation rate for the larger upsilon(TS) states was interpreted as a result of trapping of a wave function in the in-phase stretching or the CO stretching vibrational motion suppressing the motion along the dissociation coordinate. All six main peaks in the PHOFEX spectra exhibited a characteristic asymmetric profile, originating from the interference between the zero-order discrete states for the in-phase stretching vibration at the transition state and the zero-order continuum states corresponding with the motion along the dissociation coordinate. In the main progression of the PHOFEX spectra, the reversal of the asymmetry direction was also observed. This q-reversal phenomenon was ascribed to the characteristic shape of the excited (1) Sigma(+) PES near the transition region which causes a phase shift in the wave functions in a narrow energy range.

DOI： 10.1021/jp962423m

Photodissociating small polyatomic molecules in the VUV region: Resonances in the (1)Sigma(+)-(1)Sigma(+) band of OCS Reviewed

K Yamanouchi, K Ohde, A Hishikawa, DM Neumark

CHEMICAL REACTIONS AND THEIR CONTROL ON THE FEMTOSECOND TIME SCALE XXTH SOLVAY CONFERENCE ON CHEMISTRY Vol. 101 page： 789 - 797 1997

Radiative lifetime measurements of the B2∑+ state of BaH by laser spectroscopy Reviewed

L. E. Berg, K. Ekvall, A. Hishikawa, S. Kelly

Physica Scripta Vol. 55 ( 3 ) page： 269 - 272 1997

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Swedish Academy of Sciences

By applying laser resonance methods in the near infrared wavelength region around 900 nm, a time-resolved experiment has been performed on the low lying B 2∑+ state of barium hydride. The radiative lifetime is shown to vary with the rotational quantum number due to perturbations between the low lying A′ 2Δ, A 2∏ and B 2∑+ states. The following lifetime was obtained for the BaH molecule, where local perturbations are assumed to be negligible: τ(B 2∑+(ν′ = 0, J = 5.5)) = 125 ± 2 ns.

DOI： 10.1088/0031-8949/55/3/003

Laser spectroscopy of SrH. Time-resolved measurements of the A(2)Pi state Reviewed

LE Berg, K Ekvall, A Hishikawa, S Kelly, C McGuinness

CHEMICAL PHYSICS LETTERS Vol. 255 ( 4-6 ) page： 419 - 424 1996.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

In the near-infrared and red wavelength region around 680-760 nm, the spectrum of the A(2) Pi-X(2) Sigma transition of gaseous SrH appears. By applying laser spectroscopic methods, a time-resolved experiment has been performed on the low-lying A(2) Pi state of strontium hydride. No local influences on the A(2) Pi state were found due to interactions with the low-lying A'(2) Delta state, as in the case of the BaH molecule. The following zero-pressure lifetime was obtained for the SrH molecule: tau(A(2) Pi(1/2) (upsilon'=0))=33.8+/-1.9 ns.

DOI： 10.1016/0009-2614(96)00376-4

VUV photofragment excitation spectroscopy: Dynamics on dissociative potential surface of OCS Reviewed

K Ohde, A Hishikawa, K Yamanouchi

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Vol. 79 page： 433 - 436 1996.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The measurements of the photofragment excitation (PHOFEX) spectrum of jet-cooled OCS were extended toward the 152.6 and 150.6 nm peaks in the (1) Sigma(+)-(1) Sigma(+) transition. The PHOFEX spectra were recorded by scanning the wavelength of a tunable vacuum ultraviolet (VU) photolysis laser while probing the S(S-1) product by a second laser. Due to the efficient cooling of the sample in the free-jet expansion and the high-resolving power of the VUV laser, the homogeneous broadening of the dissociative state was derived directly from the observed PHOFEX spectrum. Based on the measured peak width, the lifetimes (tau) of the dissociative states at 152.6 and 150.6 nm were determined to be tau approximate to 50 and 31 fs. The PHOFEX peaks were found to exhibit an asymmetric line profile, and a fitting to a Fano line formula led to the asymmetry parameters, q= -8.1(2) and -13.0(6), for the 152.6 and 150.6 nm peaks, indicating a considerable mixing of the continuum and discrete states in that particular energy region. On the basis of the determined lifetimes and q values, together with the corresponding values for the 154.5 nm peak, tau approximate to 140 fs and q = -3.5(9), the dissociation dynamics on the repulsive (1) Sigma(+) surface was inferred.

DOI： 10.1016/0368-2048(96)02888-5

PHOTODISSOCIATION AND VIBRATIONAL DYNAMICS OF OCS IN THE VUV REGION Reviewed

K YAMANOUCHI, K OHDE, A HISHIKAWA, CD PIBEL

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 68 ( 9 ) page： 2459 - 2464 1995.9

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

The photofragment excitation (PHOFEX) spectrum of jet-cooled OCS was remeasured for the 154.5 nm peak in the (1) Sigma(+)-(1) Sigma(+) transition by scanning a tunable vacuum ultraviolet (VUV) laser wavelength in the deep VUV region and by probing the S(S-1) product with a second laser. Due to the efficient cooling of the sample in the free-jet expansion and the high-resolving power of the VUV laser, the homogeneous broadening of the dissociative state was derived directly from the observed PHOFEX spectrum. Based on the measured peak width, the lifetime (tau) of the dissociative state was determined to be tau congruent to 0.14 ps. The profile of the PHOFEX peak was found to be asymmetric and was fit to a Fano line profile to derive the value of the asymmetry parameter, q=-3.5(9), which indicates a considerable mixing of the continuum and discrete states in that particular energy region. A Fourier-transform analysis was also performed for the whole distinct absorption feature in the 160-140 nm region measured by McCarthy and Vaida [J. Phys. Chem., 92, 5875 (1988)], and the period of the vibrational motion on the dissociative potential-energy surface was derived to be 41 fs. Using these pieces of experimental evidence, the dissociation dynamics on the repulsive (1) Sigma(+) surface in the 154.5 nm region was inferred.

DOI： 10.1246/bcsj.68.2459

MONTE-CARLO STUDY OF POPULATION AND ALIGNMENT RELAXATION BY TRAPPED LINE RADIATION Reviewed

A HISHIKAWA, T FUJIMOTO, P ERMAN

PHYSICAL REVIEW A Vol. 52 ( 1 ) page： 189 - 196 1995.7

ENERGY-DEPENDENT COLLISION CROSS-SECTION AS ESTIMATED FROM TEMPERATURE-DEPENDENT RATE COEFFICIENT - DISALIGNMENT OF EXCITED NEON ATOMS BY NEON COLLISIONS Reviewed

Y ISHITANI, H ISHIDA, T KITAGAWA, A HISHIKAWA, T FUJIMOTO

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 26 ( 19 ) page： L671 - L675 1993.10

Language：English Publisher：IOP PUBLISHING LTD

Laser-induced-fluorescence spectroscopy has been applied to a neon discharge plasma. A disalignment rate coefficient for 2p2 (Paschen notation; 2p5 3p configuration) atoms for neon atom collisions was determined at several atom temperatures (77-640 K). From the temperature dependence of the rate coefficient we estimate the cross section which explicitly depends on collision energy. It is found that the cross section has a positive energy dependence, which suggests that the OMEGA = 0 and 1 molecular potential curves correlating to the 2P2 State of neon are repulsive by about 100 cm-1 where these curves split by 10-20 cm-1.

DOI： 10.1088/0953-4075/26/19/007

LIFETIME MEASUREMENTS OF EXCITED MOLECULAR-STATES USING A TI-SAPPHIRE LASER - RADIATIVE LIFETIMES OF THE A(2)PI,B(2)SIGMA(+), AND C(2)PI STATES OF BACL Reviewed

LE BERG, A HISHIKAWA, A KARAWAJCZYK, T OLSSON

JOURNAL OF MOLECULAR SPECTROSCOPY Vol. 160 ( 2 ) page： 593 - 595 1993.8

LIFETIME MEASUREMENTS OF EXCITED MOLECULAR-STATES USING A TI SAPPHIRE LASER RADIATIVE LIFETIMES OF THE A(2)PI, B(2)SIGMA(+) AND C(2)PI STATES OF BAF Reviewed

LE BERG, T OLSSON, JC CHANTELOUP, A HISHIKAWA, P ROYEN

MOLECULAR PHYSICS Vol. 79 ( 4 ) page： 721 - 725 1993.7

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

A time resolved experiment on the lowest lying states of barium fluoride has been performed by applying laser resonance methods in the near infrared and green-blue wavelength regions. The A2PI and B2SIGMA+ states have been examined using Ti:sapphire laser excitations in the 710-850 nm wavelength region. The C2PI state was examined using the 496.5 nm Ar+ laser line and the lifetime of this state was in accordance with earlier measurements. The lifetimes obtained for the BaF molecule were: A2PI3/2, 46.1 +/- 0.9 ns; B2SIGMA+, 41.7 +/- 0.3 ns.

DOI： 10.1080/00268979300101571

LIFETIME MEASUREMENTS OF EXCITED MOLECULAR-STATES USING A TI-SAPPHIRE LASER - RADIATIVE LIFETIMES OF THE B(2)SIGMA+ STATE AND C(2)PI STATE OF BABR Reviewed

LE BERG, K EKVALL, E HEDIN, A HISHIKAWA, A KARAWAJCZYK, S KELLY, T OLSSON

CHEMICAL PHYSICS LETTERS Vol. 209 ( 1-2 ) page： 47 - 51 1993.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The barium bromide monohalide has been studied by using laser resonance methods in the near-infrared and green-blue wavelength regions. The low-lying B 2SIGMA+ state has been investigated in a time-resolved experiment using a Ti:sapphire laser operating around 900 nm. No influence on the radiative lifetime due to the B 2SIGMA interaction with the A'2DELTA-A 2PI complex was observed. The radiative lifetime of the C2PI state was examined using the 514.5 nm Ar+ laser line. The derived lifetime of this state was in agreement with earlier measurements. The following lifetimes were obtained for the BaBr molecule: B 2SIGMA+ 123.2 +/- 0.5 ns and C2PI(3/2)16.9+/-0.1 ns.

DOI： 10.1016/0009-2614(93)87199-d

PREDISSOCIATION EFFECTS IN THE A2-DELTA AND B2-SIGMA- STATES OF CD Reviewed

M DANIELSSON, P ERMAN, A HISHIKAWA, M LARSSON, E RACHLEWKALLNE, G SUNDSTROM

JOURNAL OF CHEMICAL PHYSICS Vol. 98 ( 12 ) page： 9405 - 9411 1993.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Lifetimes have been measured for a large number of rotational levels of the A2DELTA and B2SIGMA-states in CD using the high frequency deflection technique. Four B-state levels are found to be influenced by predissociation by rotation which demands a lower value of the CD dissociation energy. The B state predissociations have also been studied using ab initio calculations. The A state levels above the dissociation limit are found to be weakly predissociated through interaction with the ground state continuum. The results are compared with earlier lifetime investigations of CH.

DOI： 10.1063/1.464372

THE ELECTRONIC-TRANSITION MOMENT AND THE OSCILLATOR STRENGTH OF THE SIH+ A1-PI-X1-SIGMA+ TRANSITION Reviewed

A HISHIKAWA, A KARAWAJCZYK

JOURNAL OF MOLECULAR SPECTROSCOPY Vol. 158 ( 2 ) page： 479 - 481 1993.4

EXPERIMENTAL-OBSERVATION OF DISALIGNMENT EFFECTS IN RADIATION TRAPPING PROCESSES Reviewed

P ERMAN, A HISHIKAWA

PHYSICA SCRIPTA Vol. 46 ( 4 ) page： 348 - 353 1992.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SWEDISH ACAD SCIENCES

Alignment effects at electron excitation measurements of atomic lifetimes have been studied at 20 keV energy using the High Frequency Deflection technique and a plastic polarizer. Disalignment associated with radiation trapping is observed directly for the first time. It has been pointed out that our previous results of the lifetime of the Ar 2p(i) levels might possibly have been influenced not only by radiation trapping itself but also by this "radiative disalignment". However, this influence has been found to be negligible thanks to small intrinsic alignment in almost all lines of noble gases investigated.

DOI： 10.1088/0031-8949/46/4/006

INFLUENCE OF RADIATION TRAPPING ON THE POLARIZATION DEGREE OF THE HE-I 501.6 NM LINE IN COLLISION SPECTROSCOPY Reviewed

A HISHIKAWA, H MIZUNO, M TANI, R OKASAKA

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 25 ( 16 ) page： 3419 - 3431 1992.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The influence of radiation trapping on the polarization degree of the emission of the He I 501.6 nm line (3(1)P-2(1)S) is studied by experiments and a simulation. In the experiments, a particle (proton or electron) beam was injected into a helium gas cell. The accelerating energy was 100 keV for protons and 1.5, 2.5 and 5.0 keV for electrons. The polarization degree measured as a function of gas pressure showed a minimum at a certain gas pressure in accordance with results obtained by Hasselkamp et al. A Monte Carlo simulation method to treat the non-resonance line of the resonance state in a finite gas cell is presented. This simulation reproduces the minimum of the polarization degree as seen from experiments. We conclude that this minimum is caused by the asymmetry in the spatial distribution of atoms excited by collisions. We attempt to estimate a polarization degree not influenced by radiation trapping by fitting the simulated results to the experimental ones.

DOI： 10.1088/0953-4075/25/16/004

The g-u interference oscillations observed in the emission cross sections and the optical polarizations in he+—he collisions Reviewed

M. Tani, A. Hishikawa, R. Okasaka

Journal of Physics D: Applied Physics Vol. 24 ( 6 ) page： 1359 - 1376 1991.3

Language：English Publishing type：Research paper (scientific journal)

We have observed emission radiation from helium atoms excited in He+-He collisions by the direct and electron capture processes over the energy range 0.5-20 keV.The relative emission cross sections for transitions 21,3P-31,3S, 21,3S-31,3P and 21,3P-31,3Dhave been determined. Degrees of optical polarization have also been determined for theP- and D-state excitations. The emission cross section of the direct excitation and that ofthe electron capture excitation show oscillations against impact energy, which are inantiphase with each other. The polarization degrees for both processes are of nearly thesame magnitude and show weak oscillations in antiphase with each other. The oscillationsof the cross section and those of the polarization degree are in phase in some cases andin antiphase in other cases. These oscillations are interpreted as due to the interferencebetween the gerade and ungerade states of the helium quasimolecular ion. From theamplitude ratio and the phase correlation between the oscillations of the cross section andthose of the polarization degree we find that the predominant g-u interference pai r is nΠg-Πu. © IOP Publishing Ltd.

DOI： 10.1088/0953-4075/24/6/022

THE G-U INTERFERENCE OSCILLATIONS OBSERVED IN THE EMISSION CROSS-SECTIONS AND THE OPTICAL POLARIZATIONS IN HE+-HE COLLISIONS Reviewed

M TANI, A HISHIKAWA, R OKASAKA

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Vol. 24 ( 6 ) page： 1359 - 1376 1991.3

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We have observed emission radiation from helium atoms excited in He+-He collisions by the direct and electron capture processes over the energy range 0.5-20 keV. The relative emission cross sections for transitions 2(1,3)P-3(1,3)S, 2(1,3)S-3(1,3)P and 2(1,3)P-3(1,3)D have been determined. Degrees of optical polarization have also been determined for the P- and D-state excitations. The emission cross section of the direct excitation and that of the electron capture excitation show oscillations against impact energy, which are in antiphase with each other. The polarization degrees for both processes are of nearly the same magnitude and show weak oscillations in antiphase with each other. The oscillations of the cross section and those of the polarization degree are in phase in some cases and in antiphase in other cases. These oscillations are interpreted as due to the interference between the gerade and ungerade states of the helium quasimolecular ion. From the amplitude ratio and the phase correlation between the oscillations of the cross section and those of the polarization degree we find that the predominant g-u interference pairs is PI-g-PI-u.

DOI： 10.1088/0953-4075/24/6/022

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