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

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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

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

DOI： 10.1103/PhysRevA.107.L021101

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

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

DOI： 10.1016/j.elspec.2022.147280

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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

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

UV-photo-excitation of formaldehyde molecules will not only lead to conventional radical or molecular dissociation following the direct path. Additionally, a hindered dissociation, roaming, occurs which we observed directly and in real-time using Coulomb explosion imaging.

Scopus

Publisher：CLEO: Fundamental Science, CLEO:FS 2023  

UV-photo-excitation of formaldehyde molecules will not only lead to conventional radical or molecular dissociation following the direct path. Additionally, a hindered dissociation, roaming, occurs which we observed directly and in real-time using Coulomb explosion imaging.

DOI： 10.1364/CLEO_FS.2023.ftu4m.1

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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

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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 (CF₄) is sensitive to the helicity of the circularly polarized laser fields.

DOI： 10.1039/d1cp05858d

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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

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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

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Language：English   Publisher：Optics InfoBase Conference Papers  

Electron-ion coincidence spectroscopy is powerful to elucidate tunneling ionization dynamics, but applicable only to molecules susceptible to dissociation. Here we introduce a novel scheme with additional pulses, which has been successfully applied to O2 HOMO-1.

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Publisher：Optics InfoBase Conference Papers  

To extend application of ω-2ω intense field reaction control to highly symmetric molecules, CF4 was studied by three-dimensional momentum imaging. The C-F bond directed along larger side of the laser fields tends to be broken.

Scopus

Publisher：Optics InfoBase Conference Papers  

Roaming molecular fragments in the prototypical formaldehyde dissociation-reaction are directly observed in real-time, using Coulomb explosion imaging and state-of-the-art theoretical modeling. How does the preparation of population ready to roam depend on the pump wavelength?

Scopus

Publisher：Optics InfoBase Conference Papers  

Using phase-locked two-color laser fields, control of fragment ejection direction and selective bond scission of OCS are demonstrated. Post-ionization interaction plays an important role in the dissociation of polar molecules.

Scopus

Publishing type：Research paper (international conference proceedings)   Publisher：Optica Publishing Group  

To extend application of ω-2ω intense field reaction control to highly symmetric molecules, CF₄ was studied by three-dimensional momentum imaging. The C-F bond directed along larger side of the laser fields tends to be broken.

DOI： 10.1364/up.2022.w2b.1

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

DOI： 10.1021/acsomega.1c04354

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

DOI： 10.1103/PhysRevA.104.023102

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

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

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

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

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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

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Language：Japanese   Publisher：Optics InfoBase Conference Papers  

"Roamers" are directly observed in the prototypical roaming reaction in the formaldehyde molecule. Despite their statistical nature, roaming is well discriminated from the radical- and molecular dissociation channels, using Coulomb explosion imaging and theoretical modeling.

DOI： 10.1364/UP.2020.Th4A.1

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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

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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

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

DOI： 10.1103/PhysRevLett.124.193201

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

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

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

DOI： 10.1364/OE.27.019702

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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

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

DOI： 10.1246/cl.170613

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+ -&gt; 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

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

DOI： 10.1063/1.4964775

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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) -&gt; NO+ + e(-) -&gt; 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

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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

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

Coulomb explosion of CO2, CO2 -&gt; CO2+2 + 2e(-) -&gt; 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

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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

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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

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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 (&lt;= 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

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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

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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+ -&gt; (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

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

Dissociative-ionization of NO, NO -&gt; NO+ + e(-) -&gt; 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

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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

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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

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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

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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

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Language：English   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/j.elspec.2014.07.013

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Language：English   Publisher：IOP PUBLISHING LTD  

DOI： 10.1088/0953-4075/47/12/120201

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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

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Other Link： http://orcid.org/0000-0003-1444-8917

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

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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

Scopus

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

Scopus

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

Scopus

Language：Japanese   Publisher：Optics InfoBase Conference Papers  

Intensity dependence of polarized He (21P) atoms in intense NIR laser fields are investigated by single-shot photoelectron spectroscopy, revealing two-photon Rabi oscillations between the initial 1s2p and 1snf (n = 5,6) Rydberg states. © 2014 OSA.

DOI： 10.1364/up.2014.08.tue.p2.4

Scopus

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

Scopus

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

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Scopus

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

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Scopus

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

DOI： DOI: 10.1103/PhysRevA.88.023421]

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

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Scopus

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

Open Access

Web of Science

Scopus

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

Open Access

Web of Science

Scopus

Publisher：Springer Berlin Heidelberg  

DOI： 10.1007/978-3-642-35052-8_9

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

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Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： DOI: 10.1016/j.elspec.2011.10.002

Authorship：Lead author   Language：Japanese  

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)) --&gt; 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

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Scopus

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

Web of Science

Scopus

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

Scopus

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

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Scopus

PubMed

Language：Japanese  

Language：Japanese  

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

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PubMed

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

Open Access

Web of Science

Scopus

PubMed

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

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

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

Web of Science

Scopus

PubMed

Language：Japanese  

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 -&gt; Ar(+) + e(-) and Ar(+) + 2h nu -&gt; 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

Web of Science

Scopus

PubMed

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

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

Web of Science

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

Web of Science

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.

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.

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

Scopus

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+)-&gt; 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

Web of Science

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

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

Web of Science

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

Web of Science

Language：English   Publisher：AMERICAN PHYSICAL SOC  

DOI： 10.1103/PhysRevLett.98.019901

Web of Science

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

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

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

Web of Science

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

Scopus

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+) -&gt; 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

Web of Science

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+) -&gt; 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

Web of Science

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

Web of Science

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

Web of Science

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

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.

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+-&gt; 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 &gt; 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+-&gt; N++NO2+-&gt; N++N++O+. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.2032988

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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+-&gt;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

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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

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

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+ --&gt; CH3-n+ +HnCN+ and CD3CN2+ --&gt; 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

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The non-sequential three-body Coulomb explosion, CS23+ --&gt; 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

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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.

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.

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.

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

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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

Scopus

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+ --&gt; 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

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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

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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.

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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+ --&gt; S+ + C+ + S+, is reconstructed from the measured momentum vectors of the fragment ions. The mean C-S bond length of &lt;r &gt; = 2.5 Angstrom and the azimuthally averaged S-C-S bond angle, &lt; gamma &gt; = 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

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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

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The dissociation processes, O-2(+)--&gt;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

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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

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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 (+))--&gt; 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

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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)+ --&gt; 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

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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)+ --&gt; 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 &lt;O-C-O angle distribution of CO2 Spreads significantly (FWHM similar to 40 degrees), and the &lt;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.

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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+--&gt; 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

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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+ --&gt; 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

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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

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The Coulomb explosion reactions of N-2, N-2((p+q)+) --&gt; 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

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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

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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

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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

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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 (&lt;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

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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

Web of Science

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

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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)) --&gt; 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

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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 --&gt; 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

Web of Science

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

Web of Science

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

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Language：English   Publisher：JOHN WILEY & SONS INC  

DOI： 10.1002/9780470141601.ch31

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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

Scopus

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

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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

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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

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

DOI： 10.1103/PhysRevA.52.189

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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

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Language：English   Publisher：ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

DOI： 10.1006/jmsp.1993.1206

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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

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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

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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

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Language：English   Publisher：ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

DOI： 10.1006/jmsp.1993.1091

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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

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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

Web of Science

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

Scopus

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

Web of Science

Language：Japanese   Publisher：Japan Synchrotron Radiation Research Institute  

DOI： 10.18957/rr.5.2.291

Language：Japanese   Publisher：The Laser Society of Japan  

Coherent light-matter interaction drives a variety of interesting processes in a quantum system. Rabioscillation is one such process offering a periodic population transfer between quantum states in anultrashort time scale. Here we demonstrate a robust and simple scheme to achieve femtosecond twophotonRabi oscillations by intense NIR laser pulses, using excited He atoms prepared by EUV-FEL.The extension to multiphoton regime will expand the applicability to highly excited or dipole-forbiddenstates.

DOI： 10.2184/lsj.45.8_493

CiNii Books

Language：Japanese  

CiNii Books

Language：Japanese   Publisher：Japan Synchrotron Radiation Research Institute  

DOI： 10.18957/rr.4.2.344

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.1.0_820

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.1.0_819

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.70.2.0_516

CiNii Books

Language：Japanese   Publisher：The Laser Society of Japan  

Laser high-order harmonics in the extreme ultraviolet (EUV) and soft X-ray region serve as a uniquetool to study ultrafast molecular dynamics associated with valence or inner-shell electron excitations.The harmonics are often obtained as a train of pulses, which result in a spectrum with a comb consistingof the odd harmonic orders. However, it is often the case that isolated pulses rather than pulse trains arepreferred in the conventional pump-probe spectroscopy, to avoid signal overlaps associated with differentharmonic orders. Here we review our approach for the single-order harmonics generation in EUV byusing dielectric multilayer mirrors and metal foils, and the application to photoelectron spectroscopy onwavepacket dynamics of simple molecules such as Br2, I2 and N2.

DOI： 10.2184/lsj.43.12_818

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.69.1.2.0_182_1

CiNii Books

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.1.2.0_215_4

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.2.2.0_170_2

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.68.1.2.0_214_4

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

The advances in free electron laser (FEL) technology allow us to generate intense laser fields in extreme ultraviolet (EUV) and X-ray. Recent studies show that responses of materials to such high-frequency intense laser fields are inherently different from those observed in visible and infrared. In this reveiw, we discuss current progresses in intense laser field physics in EUV and X-ray, especially by focussing on non-linear responses of isolated atoms.

DOI： 10.11316/butsuri.68.12_794

CiNii Books

Language：Japanese  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

Language：Japanese  

Multiphoton ionization is a typical nonlinear response of atoms in intense EUV laser fields. Single-shot photoelectron spectroscopy utilizing with a magnetic-bottle-type electron spectroscopic technique is a useful means to study the details of multiphoton multiple ionization processes. We present that the method enables us to monitor the fluctuation of SASE-FEL spectra and to derive photon energy dependence of the multiphoton multiple ionization processes precisely.

CiNii Books

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.67.1.2.0_227_1

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.67.1.2.0_227_2

CiNii Books

Language：Japanese   Publisher：The Laser Society of Japan  

Molecules exposed to few-cycle intense laser fields (> 10¹⁴ W/cm²) undergo a rapid bond breakingprocess called Coulomb explosion. Since the momenta of the resultant fragment ions reflect thegeometrical structure of the target molecule, Coulomb explosion provides a direct access to theinstantaneous structure of molecules during chemical reaction. Combined with the pump-probe schemein ultrafast spectroscopy, Coulomb explosion imaging serves as a unique means to probe ultrafastmolecular reaction processes in real time. Here we review this novel approach in ultrafast spectroscopy,with the applications to ultrafast isomerization of deuterated acetylene dication (C₂D₂²⁺).

DOI： 10.2184/lsj.40.10_745

CiNii Books

Language：Japanese   Publisher：日本工業出版  

CiNii Books

Language：Japanese   Publisher：日本工業出版  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.1.2.0_160_4

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.66.1.2.0_161_1

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.65.2.2.0_147_2

CiNii Books

Language：Japanese  

CiNii Books

Language：Japanese   Publisher：丸善  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.63.1.2.0_163_2

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research  

The structures of rotational and vibrational energy levels and the term symbols to classify different electronic states are described for diatomic molecules. Different classes of parity, (+/&minus;), (e/f) and (s/a), associated with each rovibronic level are discussed. The transition probability, the Franck-Condon factors, the H&ouml;nl-London factors and the transition moments of electronic transitions and their selection rules are described.

DOI： 10.1585/jspf.80.742

CiNii Books

Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10455609

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：社団法人 日本分光学会  

DOI： 10.5111/bunkou.52.36

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.58.1.2.0_152_3

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.58.1.2.0_152_4

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：English   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.57.1.2.0_124_2

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.57.2.2.0_123_4

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：社団法人 日本分光学会  

DOI： 10.5111/bunkou.50.76

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/butsuri1946.56.2

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.56.2.2.0_83_2

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.56.1.2.0_124_1

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

CiNii Books

Language：Japanese   Publisher：The Spectroscopical Society of Japan  

DOI： 10.5111/bunkou.49.62

CiNii Books

Language：Japanese   Publisher：学会出版センタ-  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.55.2.2.0_97_1

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.55.2.2.0_97_4

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.55.2.2.0_97_3

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.53.2.4.0_874_2

CiNii Books

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.53.1.4.0_769_3

CiNii Books

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.53.1.4.0_769_2

CiNii Books

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.53.2.2.0_343_1

CiNii Books

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.53.2.2.0_344_3

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.53.2.4.0_874_3

CiNii Books

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyog.49.4.0_70_2

CiNii Books

Language：Japanese   Publisher：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyoj.1993.4.0_54_1

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyog.48.4.0_64_1

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyoa.1991.4.0_28_1

CiNii Books

Event date： 2022.12

Language：English  

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Event date： 2022.9

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Event date： 2022.9

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Event date： 2022.9

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Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2021.12

Language：English   Presentation type：Oral presentation (invited, special)  

Event date： 2021.10 - 2022.10

Language：Japanese  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2021.9

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2021.6

Language：English   Presentation type：Oral presentation (invited, special)  

Event date： 2021.6

Language：English   Presentation type：Oral presentation (invited, special)  

Event date： 2021.6

Language：English   Presentation type：Oral presentation (general)  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.3

Language：English   Presentation type：Poster presentation  

Event date： 2021.3

Language：English   Presentation type：Poster presentation  

Event date： 2021.3

Language：English   Presentation type：Poster presentation  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)