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

Since the discovery of roaming as an alternative molecular dissociation pathway in formaldehyde (H₂CO), 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.

DOI： 10.1126/science.abc2960

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PubMed

Language：Japanese   Publisher：Physical Review Letters  

Ultrafast multiphoton ionization of Xe in strong extreme ultraviolet free-electron laser (FEL) fields (91 eV, 30 fs, 1.6×1012 W/cm2) has been investigated by multielectron-ion coincidence spectroscopy. The electron spectra recorded in coincidence with Xe4+ show characteristic features associated with two-photon absorption to the 4d-2 double core-hole (DCH) states and subsequent Auger decay. It is found that the pathway via the DCH states, which has eluded clear identification in previous studies, makes a large contribution to the multiple ionization, despite the long FEL pulse duration compared with the lifetime of the 4d core-hole states.

DOI： 10.1103/PhysRevLett.124.193201

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

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

DOI： 10.1038/NPHOTON.2015.228

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Language：Japanese   Publisher：Optics InfoBase Conference Papers  

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：Japanese   Publisher：Optics InfoBase Conference Papers  

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：Japanese   Publisher：Optics InfoBase Conference Papers  

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

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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：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.elspec.2011.10.002

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Publishing type：Research paper (scientific journal)  

This review outlines advances that have been made in recent years (2005-2007) in the study of ultrafast dynamics occurring in physical, chemical and biological research fields by using pump-probe techniques. Special emphasis is placed on coherent phenomena in materials and experimental achievements of coherent control of wave packets dynamics. After a brief theoretical description of pump-probe methods, an overview of nuclear and electronic coherences appearing in pump-probe spectroscopy is presented. Some of the highlights include molecular alignments, wave packet interferometry, hydrogen migration, and attosecond electron dynamics. © 2008 The Royal Society of Chemistry.

DOI： 10.1039/b703983m

Scopus

Language：Japanese   Publisher：ROYAL SOC CHEMISTRY  

We perform time resolved pump-probe spectroscopy on small halogen molecules ClF, Cl-2, Br-2, and I-2 embedded in rare gas solids (RGS). We find that dissociation, angular depolarization, and the decoherence of the molecule is strongly influenced by the cage structure. The well ordered crystalline environment facilitates the modelling of the experimental angular distribution of the molecular axis after the collision with the rare gas cage. The observation of many subsequent vibrational wave packet oscillations allows the construction of anharmonic potentials and indicate a long vibrational coherence time. We control the vibrational wave packet revivals, thereby gaining information about the vibrational decoherence. The coherence times are remarkable larger when compared to the liquid or high pressure gas phase. This fact is attributed to the highly symmetric molecular environment of the RGS. The decoherence and energy relaxation data agree well with a perturbative model for moderate vibrational excitation and follow a classical model in the strong excitation limit. Furthermore, a wave packet interferometry scheme is applied to deduce electronic coherence times. The positions of those cage atoms, excited by the molecular electronic transitions are modulated by long living coherent phonons of the RGS, which we can probe via the molecular charge transfer states.

DOI： 10.1039/b609058n

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

Femtosecond dynamics of molecular vibrations as well as cage motions in the B <- X transition of Cl-2 in solid Ar have been investigated. We observed molecular vibrational wave-packet motion in experimental pump-probe spectra and an additional oscillation with a 500 fs period which is assigned to the zone-boundary phonon of the Ar crystal. The cage motion is impulsively driven by the B <- X transition due to the expansion of the electronic cloud of the chromophore. To clarify the underlying mechanism, we performed simulations based on the diatomics-in-molecules method which takes into account the different shapes of the Cl-2 electronic wave function in the B and X states as well as the anisotropic interaction with the matrix. The simulation results show that Ar atom motion in the (100) plane is initiated by the electronic transition and that only those Ar atoms oscillate coherently with an similar to 500 fs period which are essentially decoupled from the molecular vibration. Their phase and time evolution are in good agreement with the experimentally observed oscillation, supporting the assignment as a displacive excitation of coherent phonons. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2147241

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/b509153e

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

Nuclear spin selection rule was investigated in the photochemical reaction of CH3 and solid parahydrogen. Conservation of nuclear spin during the reaction was examined by the intensity distribution of the rotation-vibration spectrum of methane produced by the reaction. The methyl radical CH3 was produced by in situ ultraviolet (UV) photolysis of methyl iodide CH3I embedded in solid parahydrogen. The results showed that the population of each nuclear spin state of methane was different from that of the statistical ratio. This indicated that a nuclear spin selection rule existed in the reaction.

DOI： 10.1063/1.1480003

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.elspec.2022.147280

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Authorship：Lead author,　Corresponding author   Language：Japanese   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 (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

Scopus

Publisher：Optics InfoBase Conference Papers  

DOI： 10.1364/UP.2020.Th4A.1

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of 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：Japanese   Publishing type：Research paper (scientific journal)   Publisher：International Union of Crystallography (IUCr)  

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

DOI： 10.1364/OE.27.019702

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

DOI： 10.1016/j.elspec.2018.07.001

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Authorship：Lead author   Language：Japanese  

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

DOI： 10.1039/c6cp07471e

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

DOI： 10.1063/1.4964775

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

DOI： 10.1103/PhysRevLett.116.163002

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

DOI： 10.1088/0953-4075/49/3/034005

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

DOI： 10.1016/j.elspec.2015.12.010

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

DOI： 10.11316/jpsgaiyo.71.1.0_819

CiNii Books

Language：Japanese   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 (<= 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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Other Link： http://orcid.org/0000-0003-1444-8917

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

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

DOI： 10.1063/1.4938821

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

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

DOI： 10.1088/1742-6596/635/11/112027

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

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

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

DOI： 10.1103/PhysRevA.90.053403]

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

DOI： 10.1103/PhysRevA.90.053403

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

DOI： 10.1088/0953-4075/47/19/195602

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Language：Japanese   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

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

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

DOI： 10.1103/PhysRevA.88.063422

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

DOI： 10.1103/PhysRevA.88.023421

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Language：Japanese   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

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Language：Japanese   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

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jp301367j

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Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp301367j

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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

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

DOI： 10.1103/PhysRevLett.107.243003

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

DOI： 10.1063/1.3648133

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

DOI： 10.1364/OE.19.009600

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

DOI： 10.1039/c0cp02333g

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Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jms.2011.04.014

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

DOI： 10.1103/PhysRevLett.105.133001

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

Vibronic progressions are programmed into a pulse shaper which converts them via the inherent Fourier transformation into a train of femtosecond pulses in time domain for chromophore excitation. Double Pulse results agree with phase-sensitive wave packet superposition from a Michelson interferometer which delivers coherence times with high reliability. Spectral resolution of 1 nm and a spacing of around 4 nm within the 20 nm envelope centered at 590 nm delivers a train of seven phase-controlled 40 fs subpulses separated by 250 fs. Combs adjusted to the zero phonon lines (ZPL) and phonon sidebands (PSB) of the B state vibronic progression are reproduced in the chromophore for a coherent subpulse accumulation. B state ZPL wave packet dynamics dominates in pump-probe spectra due to its coherence despite an overwhelming but incoherent A state contribution in absorption. PSB comb accumulation is also phase sensitive and demonstrates coherence within several 100 matrix degrees of freedom in the vicinity.

DOI： 10.1021/jp900287m

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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 (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.

DOI： 10.1021/jp806466x

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

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

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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

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Publishing type：Research paper (scientific journal)  

Femtosecond pump-probe 2D (wavelength and delay) optical Kerr effect (OKE) spectroscopy is used to measure laser induced birefringence in parahydrogen and normal hydrogen crystals at 4.2 K. At the probe center wavelength the OKE signal reveals underdamped sinusoidal modulations at frequencies corresponding to the Raman-active transverse optical phonon mode of solid parahydrogen (36.8 cm-1) and normal hydrogen (38.5 cm-1), respectively. For parahydrogen crystals, at small shifts away from the probe center wavelength the OKE signal displays high frequency oscillations (355 cm-1) which correspond to J = 2 rotons with a 94 fs time period. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2008.04.123

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Publishing type：Research paper (scientific journal)  

Electronic and vibrational coherences in the B 3Π(0 +u) ← X1Σ+g transition of chlorine (Cl2) molecules doped in an argon matrix are investigated by exciting with a pulse pair whose relative phase is scanned for every time delay step. The spacing and position of the generated spectral comb are controlled by the delay and relative phase of the pulses. The B 3Π(0+u) ← X1Σ +g excitation spectrum shows a progression of zero phonon lines which are decoupled from the lattice and of phonon side bands which originate from a concerted excitation of intramolecular and lattice vibrations. The molecular anharmonicity is compensated for by applying a negative chirp difference of the two pulses, which leads to an asymmetry in the signal around time zero. Absolute phase values are determined from spectral positions in the measured comb patterns. They are used to calculate fringe patterns and to simulate interferograms by a multiplication with the excitation spectrum which are compared with the measured ones in detail. From simulated interferograms of zero phonon lines and phonon side bands, we show that the two contributions can be selected with a large contrast by a time delay of two molecular vibrational periods. © 2008 IOP Publishing Ltd.

DOI： 10.1088/0953-4075/41/7/074013

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Publishing type：Research paper (scientific journal)  

The nuclear spin conversion of C H4 and C D4 isolated in solid parahydrogen was investigated by high resolution Fourier transform infrared spectroscopy. From the analysis of the temporal changes of rovibrational absorption spectra, the nuclear spin conversion rates associated with the rotational relaxation from the J=1 state to the J=0 state for both species were determined at temperatures between 1 and 6 K. The conversion rate of C D4 was found to be 2-100 times faster than that of C H4 in this temperature range. The faster conversion in C D4 is attributed to the quadrupole interaction of D atoms in C D4, while the conversion in C H4 takes place mainly through the nuclear spin-nuclear spin interaction. The conversion rates depend on crystal temperature strongly above 3.5 K for C H4 and above 2 K for C D4, while the rates were almost constant below these temperatures. The temperature dependence indicates that the one-phonon process is dominant at low temperatures, while two-phonon processes become important at higher temperatures as a cause of the nuclear spin conversion. © 2008 American Institute of Physics.

DOI： 10.1063/1.2889002

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

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

DOI： 10.1063/1.2828557

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Publishing type：Research paper (scientific journal)  

We demonstrate the visualization of ultrafast hydrogen migration in deuterated acetylene dication (C2D22+) by employing the pump-probe Coulomb explosion imaging with sub-10-fs intense laser pulses (9 fs, 0.13PW/cm2, 800 nm). It is shown, from the temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C2D23+→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 (∼90fs) and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevLett.99.258302

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

Photochemical reactions of molecules in solid orthodeuterium (o-D-2) have been studied by high-resolution infrared spectroscopy and compared with previous results obtained in solid parahydrogen (p-H-2). Ultraviolet photoplysis of CD3I molecules in solid o-D2 yielded CD3 radicals and iodine atoms efficiently, which indicates a small cage effect in solid o-D2, as in the case of solid p-H2. The Fourier transform infrared spectrum of the nu(3) vibrational band of CD3 showed a rotational structure with additional splitting due to crystal field interactions. The magnetic dipole transition (2P(1/2) (<-) P-2(3/2)) of the I atom isolated in solid o-D-2 was observed together with a strong rotational satellite of deuterium molecules through the electron-roton coupling in solid hydrogen. The tunneling reaction between CD3 and D-2 was not observed in a time scale of a few days, which gives the upper limit of the tunneling,reaction rate of 10(-8) s(-1) at 4.2 K.

DOI： 10.1021/jp0761113

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

We report on coherent zone-boundary phonons of solid Ar doped with Cl-2 in pump-probe spectra. Comparison with molecular dynamic simulation shows that specific motions of Ar atoms in the (100) plane are responsible for the observed oscillations.

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+) -> 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

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Web of Science

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

The ortho-to-para nuclear spin ratio of cyclopropenylidene ( cyclic C3H2) in TMC-1 cores was investigated using the 45 m radio telescope at Nobeyama Radio Observatory. We have observed four ortho lines (J(KaKc) = 2(12) - 1(01), 3(12) - 3(03), 3(21) - 3(12), and 3(30) - 3(21)) and four para lines (J(KaKc) 2(02) - 1(11), 2(11) - 2(02), 2(20) - 2(11), and 3(22) - 3(13)) of cyclic C3H2 in six cores in TMC-1. A statistical equilibrium analysis of the observed intensities revealed apparent correlation between the ortho-to-para ratio of cyclic C3H2 and chemical evolution of the molecular cloud; the ortho-to-para ratio in younger cores is less than 2, while that in older cores is close to the statistical ratio of 3. A simple chemical model calculation indicates that the correlation is ascribed to the conservation of nuclear spin angular momenta in chemical reactions relevant to the production, destruction, and reproduction of cyclic C3H2. Since cyclic C3H2 has been observed in a variety of sources, the ortho-to-para ratio of cyclic C3H2 may be a useful probe of chemical evolution of molecular clouds.

DOI： 10.1086/501041

Web of Science

Language：English   Publisher：TAYLOR & FRANCIS LTD  

Solid parahydrogen, known as a quantum crystal, is a novel matrix for the study of physical and chemical processes of molecules at low temperatures by high-resolution infrared spectroscopy. Ro-vibrational motion of molecules embedded in solid parahydrogen is well quantized on account of the weak interaction in the crystal. In addition, molecules are almost free from the cage effect because of the softness of the quantum crystal, so that a variety of chemical reactions could be observed for molecules in solid parahydrogen at liquid He temperatures. In this article, we survey our recent studies on photodissociation of methyl radicals and subsequent reactions in solid parahydrogen, and discuss ( 1) the nuclear spin selection rule in chemical reactions and ( 2) pure tunnelling reactions obtained from the analysis of the present system.

DOI： 10.1080/01442350500444107

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Despite several suggestions concerning the existence of negatively charged molecules and negative atomic ions in molecular clouds, few attempts have been made to search for negative ions in molecular clouds. In the present study, we extensively searched for three negative molecular ions (CCH-, NCO-, and NCS-) in a dark cloud, L134N, using the Nobeyama 45-m radio telescope. The three negative ions are molecules whose rotational constants have been reported based on laboratory experiments. After a long accumulation, a trace amount of an unidentified emission line was detected at a frequency close to the theoretical prediction of the J = 1-0 transition of CCH-. If this unidentified line is attributable to CCH-, the observed emission intensity would provide an estimation of the column density of CCH- in L134N to be 1.0 x 10(11) cm(-2), which corresponds to a fractional abundance of 5 x 10(-12) relative to hydrogen. However, our recent observation using the IRAM 30-m telescope did not reproduce the J = 1-0 signal, nor detect any trace of the J = 2-1 transition. Thus, the identification of CCH- in L134N is not yet confirmed. As for other ions, signals of neither NCO- nor NCS- were detected in L134N. Although we also searched for the three negative ions in a translucent cloud, CB228, and a star-forming region, SgrB2, no signals were detected. The upper limit abundances of the ions in these clouds are discussed limit abundances of the ions in these clouds are discussed.

DOI： 10.1093/pasj/57.2.325

Web of Science

Scopus

Other Link： http://orcid.org/0000-0002-0567-6881

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

The diatomic Cl-2 in solid Ar is examined to discuss the information obtained by wavepacket interferometry in condensed phase and to contrast it with femtosecond pump-probe and linear absorption spectra.

Web of Science

Web of Science

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

Tunneling chemical reactions between deuterated methyl radicals and the hydrogen molecule in a parahydrogen crystal have been studied by Fourier transform infrared spectroscopy. The tunneling rates of the reactions R+H-2-->RH+H (R=CD3,CD2H,CDH2) in the vibrational ground state were determined directly from the temporal change in the intensity of the rovibrational absorption bands of the reactants and products in each reaction in solid parahydrogen observed at 5 K. The tunneling rate of each reaction was found to differ definitely depending upon the degree of deuteration in the methyl radicals. The tunneling rates were determined to be 3.3x10(-6) s(-1), 2.0x10(-6) s(-1), and 1.0x10(-6) s(-1) for the systems of CD3, CD2H, and CDH2, respectively. Conversely, the tunneling reaction between a CH3 radical and the hydrogen molecule did not proceed within a week's time. The upper limit of the tunneling rate of the reaction of the CH3 radical was estimated to be 8x10(-8) s(-1). (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1642582

Web of Science

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

Solid parahydrogen provides a novel matrix for isolation spectroscopy of atoms and molecules. Ro-vibrational motion of molecules embedded in solid parahydrogen is well quantized on account of the weak interactions in the crystal and of the softness of the crystal being characteristic of quantum crystals. Most of the observed spectral linewidths are one or two orders of magnitude sharper than those observed in conventional rare gas matrices. The sharp linewidths make the parahydrogen crystal an excellent matrix for the study of ro-vibrational states and dynamics of dopant molecules in the condensed phase by high-resolution spectroscopy. In this article, we have summarized the most fundamental part of our study, that is, the theory of ro-vibrational states of dopant molecules in the crystal, which is necessary for the quantitative analysis of high-resolution infrared spectra. We also discuss what we have learned from the analysis of high-resolution infrared spectra in solid parahydrogen. These include perturbations to rotational motion of dopant molecules, reduction of rotational constants, vibrational dephasing and relaxation. Outstanding questions to be solved are also discussed herein. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.vibspec.2003.06.001

Web of Science

Publishing type：Research paper (scientific journal)  

The results of investigations into the suitability of condensed-phase parahydrogen as a Raman-shifting medium for infrared cavity ringdown laser absorption spectroscopy were reported. The conversion of ∼10-ns pulses of 532-nm radiation into first-, second-, and third-order vibrational Stokes radiation in bulk liquid and solid parahydrogen after a single 11-cm pass was observed. It was found that the liquid H2 yields more efficient conversion than solid H2 with certain focal geometries, and in case of the solid, a collimated or loosely focused pump geometry was more efficient than a tight focus.

DOI： 10.1063/1.1556560

Web of Science

Scopus

Publishing type：Research paper (scientific journal)  

We report the preliminary results of our experiments with stimulated Raman scattering in para-hydrogen crystal aimed at developing a continuously tunable laboratory laser source of mid-infrared radiation. With laser pulses at 532 nm, a conversion efficieney for the first Stokes beam of as much as 20% in the forward direction was observed through a single-pass, 5-cm-long crystal. Generation of mid-infrared pulses at 4.5 μm was achieved by use of the output of a near-infrared pulsed laser (1.6 μm, 3 ns), and an absorption spectrum of gaseous CD4 molecules was successfully recorded. These results suggest use of the solid para-hydrogen Raman shifter as a promising light source for mid-infrared spectroscopy. © 2003 Optical Society of America.

DOI： 10.1364/OL.28.000037

Scopus

Web of Science

Publishing type：Research paper (scientific journal)  

Diffusion of hydrogen atoms in solid parahydrogen was investigated using high-resolution infrared spectroscopy. Hydrogen atoms were produced as by-products of a photoinduced reaction of nitric oxides embedded in solid parahydrogen. The diffusion of the hydrogen atoms is mainly terminated by the reaction H+NO→HNO. The diffusion rate determined from the increase of the intensity of rotation-vibration transitions of HNO molecules was found to be two orders of magnitude larger than that determined by the self-recombination reaction of H+H→H2 in pure parahydrogen crystals. © 2003 American Institute of Physics.

DOI： 10.1063/1.1614182

Web of Science

Scopus

Publishing type：Research paper (scientific journal)  

Pure vibrational overtone transitions of solid parahydrogen are studied using high-resolution laser spectroscopy. Extremely narrow spectral linewidth (∼20MHz) allows us to observe rich spectral structure that originates in subtle intermolecular interactions in the crystal. It is found that anisotropy of the distribution of zero-point lattice vibration of hydrogen molecules perturbs the energy levels of the vibrationally excited states significantly. A large amplitude of zero-point lattice vibration, an intrinsic propoerty of quantum solids, is directly observed from the present high-resolution spectroscopy. The first observation of a pure vibrational overtone transition of solid orthodeuterium is also discussed. © 2003 American Institute of Physics.

DOI： 10.1063/1.1619353

Web of Science

Scopus

Web of Science

Publishing type：Research paper (scientific journal)  

Alkyl iodides were photolyzed in solid parahydrogen at about 5 K. The first photolysis with 253.7 nm photons yielded two products by reactions, RI + hv (253.7 nm) → Rfree + ·Ifree and (R·-·I), the latter being a complex between the radical R· and the iodine atom ·I. Subsequent photolysis with 193 nm photons activated the radical moiety in both products to induce a reaction, R· + H2 + hv (193 nm) → RH + ·H, which gave the products RHfree and (RH-·I). The radical R· and the alkane RH were characterized by the mid-IR absorption while the iodine atoms in ·Ifree and (R·-·I) and (RH-·I) were identified by the near IR absorption of the magnetic dipole transition of the atom. © 2002 Published by Elsevier Science B.V.

DOI： 10.1016/S0009-2614(02)00354-8

Scopus

Web of Science

Publishing type：Research paper (scientific journal)  

The photochemistry of (HI)m⋯(CO2)n (m, n = 1,2, ...) complexes trapped in solid parahydrogen was studied by Fourier transform infrared absorption spectroscopy. Photolysis of the HI in the HI⋯(CO2)n complexes results in the generation of carbon monoxide and water molecules along with iodine atoms. Analysis of the observed spectra leads to the conclusion that the energetic hydrogen atom produced by the photolysis of HI initiates the reaction with one of the CCh molecules in the complexes as H + CO2 → OH + CO, which is followed by the secondary reaction of OH radicals with the matrix hydrogen as OH + H2 → H2O + H. These four-atom reactions are of practical importance in combustion processes as well as of theoretical importance in fundamental chemical dynamics. The result of the present study shows the usefulness of the parahydrogen matrix for fundamental study of photochemistry with the use of weakly bound complexes. © 2000 American Chemical Society.

Scopus

Web of Science

Publishing type：Research paper (scientific journal)  

Photolysis of methyl iodide in solid parahydrogen (p-H2) at about 5 K is studied with ultraviolet light at 253.7 and 184.9 nm. It is found that the light at 253.7 nm produces only methyl radical, whereas the light at 184.9 nm yields both methyl radical and methane. The mechanism of the formation of the photoproducts is elucidated by analyzing the temporal behavior of the observed vibrational absorption. It is concluded that methyl radical in the ground state does not react with p-H2 molecules appreciably but that the radical in the electronic excited state of B̃(2A1′), accessible by reabsorption of 184.9 nm photons by the radical, decomposes to a singlet methylene CH2 ã(1A1) and a hydrogen atom (2S) and that the singlet methylene reacts with a p-H2 molecule to give methane. © 1998 American Institute of Physics.

DOI： 10.1063/1.477276

Scopus

Authorship：Lead author   Language：Japanese  

CiNii Books

Authorship：Lead author   Language：Japanese  

CiNii Books

Authorship：Lead author  

Authorship：Lead author  

Language：Japanese   Publisher：Japan Synchrotron Radiation Research Institute  

DOI： 10.18957/rr.5.2.291

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.70.2.0_516

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

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

CiNii Books

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

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

J-GLOBAL

Language：Japanese   Publisher：日本工業出版  

CiNii Books

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

CiNii Books

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

CiNii Books

Language：Japanese  

J-GLOBAL

Language：Japanese  

CiNii Books

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

CiNii Books

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

CiNii Books

Language：Japanese  

CiNii Books

Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：ROYAL SOC CHEMISTRY  

We perform time resolved pump-probe spectroscopy on small halogen molecules ClF, Cl-2, Br-2, and I-2 embedded in rare gas solids (RGS). We find that dissociation, angular depolarization, and the decoherence of the molecule is strongly influenced by the cage structure. The well ordered crystalline environment facilitates the modelling of the experimental angular distribution of the molecular axis after the collision with the rare gas cage. The observation of many subsequent vibrational wave packet oscillations allows the construction of anharmonic potentials and indicate a long vibrational coherence time. We control the vibrational wave packet revivals, thereby gaining information about the vibrational decoherence. The coherence times are remarkable larger when compared to the liquid or high pressure gas phase. This fact is attributed to the highly symmetric molecular environment of the RGS. The decoherence and energy relaxation data agree well with a perturbative model for moderate vibrational excitation and follow a classical model in the strong excitation limit. Furthermore, a wave packet interferometry scheme is applied to deduce electronic coherence times. The positions of those cage atoms, excited by the molecular electronic transitions are modulated by long living coherent phonons of the RGS, which we can probe via the molecular charge transfer states.

DOI： 10.1039/b609058n

Web of Science

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Venue：ウインクあいち   Country：Japan  

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Venue：立命館大学びわこ・くさつキャンパス   Country：Japan  

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Event date： 2021.9 - 2021.10

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Language：Japanese