810 research outputs found
Imaging Rotational Wave Packets In Molecules And Clusters
No full textIrradiation of ultrashort laser pulses onto a molecular ensemble inherently results in the creation of a quantum wave packet (WP), i.e., a coherent superposition of several (or sometimes many) eigenstates. It is an ultimate goal in modern molecular physics to establish the way for creating WPs as designed, and it is also essential for advanced WP manipulation to know how to characterize the WP experimentally.
Over the last two decades, intense nonresonant excitation has been extensively adopted to realize “nonadiabatic molecular alignment” or “nonadiabatic rotational excitation,” where the impulsive torque due to anisotropic molecular polarizability instantaneously aligns the molecules and their rotation is coherently excited in the vibronic ground-state manifold.\footnote{Y. Ohshima and Hasegawa, Int. Rev. Chem. Phys. \textbf{29}, 619 (2010).} Evolution of the rotational WP thus created can be tracked as a series of images for the time-dependent molecular orientational distribution, e.g., by implementing pump-probe Coulomb explosion ion-imaging measurements. We will represent some examples of such “molecular movies” taken with a newly developed imaging configuration,\footnote{K. Mizuse, R. Fujimoto, and Y. Ohshima, Rev. Sci. Instrum. \textbf{90}, 103107 (2019).} which is capable to clearly capture the time-dependent nodal structures, instantaneous alignment, angular dispersion, and fractional revivals of the rotational WP while the molecular ensemble keeps rotating in one direction.\footnote{K. Mizuse, K. Kitano, H. Hasegawa, and Y. Ohshima, Sci. Adv. \textbf{1}, e1400185 (2015).}
Wave-packet imaging will also be developed as a new approach in molecular spectroscopy, since energy intervals between the eigenstates that constitute the WP are encoded in the molecular movies shoot by the method. We will show some recent results along this direction; rotational spectra have been successfully extracted for homodimers of nonpolar molecules, which have been scarcely investigated because of the difficulty in recording or analyzing their microwave or infrared spectrum.Made available in DSpace on 2021-09-24T21:09:52Z (GMT). No. of bitstreams: 2
4867.pdf: 16715 bytes, checksum: 93e0a96cf96b12d7bb5ffb875ac617d5 (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
Previous issue date: 2021-06-22Made available in DSpace on 2022-01-21T16:09:48Z (GMT). No. of bitstreams: 4
4867.pdf.txt: 2210 bytes, checksum: 9ed914f99683eb6035b8e7e544df2b84 (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
4867.pdf: 16715 bytes, checksum: 93e0a96cf96b12d7bb5ffb875ac617d5 (MD5)
TG02_4867.pptx: 93257085 bytes, checksum: 2b47776a083f4344dc6390960cae3ef0 (MD5)
Previous issue date: 2021-06-2
Imaging of rotational wave packets in molecules and clusters
No full textMade available in DSpace on 2020-06-26T03:04:07Z (GMT). No. of bitstreams: 2
4387.pdf: 16716 bytes, checksum: fa0d793fb76e4488c807423c5a18f483 (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
Previous issue date: 22Irradiation of ultrashort laser pulses onto a molecular ensemble inherently results in the creation of a quantum wave packet (WP), i.e., a coherent superposition of several (or sometimes many) eigenstates. It is an ultimate goal in modern molecular physics to establish the way for creating WPs as designed, and it is also essential for advanced WP manipulation to know how to characterize the WP experimentally.
Over the last two decades, intense nonresonant excitation has been extensively adopted to realize “nonadiabatic molecular alignment” or “nonadiabatic rotational excitation,” where the impulsive torque due to anisotropic molecular polarizability instantaneously align the molecules and their rotation is coherently excited in the vibronic ground-state manifold.\footnote{Y. Ohshima and Hasegawa, Int. Rev. Chem. Phys. \textbf{29}, 619 (2010).} Evolution of the rotational WP thus created can be tracked as a series of images for the time-dependent molecular orientational distribution, e.g., by implementing pump-probe Coulomb explosion ion-imaging measurements. We will represent some examples of such “molecular movies” taken with a newly configured imaging configuration,\footnote{K. Mizuse, R. Fujimoto, and Y. Ohshima, Rev. Sci. Instrum. \textbf{90}, 103107 (2019).} which is capable to clearly capture the time-dependent nodal structures, instantaneous alignment, angular dispersion, and fractional revivals of the rotational WP while the molecular ensemble keeps rotating in one direction.\footnote{K. Mizuse, K. Kitano, H. Hasegawa, and Y. Ohshima, Sci. Adv. \textbf{1}, e1400185 (2015).}
Wave-packet imaging will also be developed as a new approach in molecular spectroscopy, since energy intervals between the eigenstates that constitute the WP are encoded in the molecular movies shoot by the method. We will show some recent results along this direction; rotational spectra have been successfully extracted for homodimers of nonpolar molecules, which have been scarcely investigated because of the difficulty in recording or analyzing their IR or microwave spectrum
VIBRONIC SPECTRA OF BENZENE CLUSTERS REVISITED: I. THE TETRAMER
No full textT. Iimori and Y. Ohshima, J. Chem. Phys. 114 2867 (2001). J. B. Hopkins, D. E. Powers and R. E. Smalley, J. Phys. Chem. 84 3739 (1981). O. Engkvist, P. Hobza, H. L. Selzle and E. W. Schlag, J. Chem. Phys. 110 5758 (1999).Author Institution: Graduate School of Science, Kyoto University; Department of Chemistry, Graduate School of Science, Kyoto UniversityWe revisit the vibronic band systems of benzene cluster isotopomers by mass-selective resonant two-photon ionization (R2PI) and ultraviolet-ultraviolet hole burning Hole burning spectra on the transitions previously assigned to the in the -localized region show that there are five distinct isotopomers having molecule(s). R2PI spectra which have similar band structure are recorded in the mass channel as well. The results indicate that the transitions are due to the cluster larger than the trimer, and thus the mass assignments that have been accepted for a couple of decades must be corrected. The number of the isomers and observed splittings are discussed in terms of the tetramer that have the geometry with four equivalent sites belonging to point group, which is also consistent with a NEMO of its most stable structure
ULTRAFAST MODE-SELECTIVE POPULATION CONTROL OF LARGE AMPLITUDE VIBRATION IN DIPHENYLMETHANE
No full textLarge-amplitude motion (LAM) may induce a substantial conformational change in molecules, which is deeply relevant to molecular functionality, e.g., in biomolecules. However, the creation and manipulation of vibrational wave packets pertinent to LAM in isolated molecular systems have been rarely realized, and most studies on molecules in the electronic ground states deal with one-dimensional LAMᵃᵇ. Here we study diphenylmethane (DPM), which has two degrees of freedom for LAM, i.e., symmetric and anti-symmetric torsional vibration, T (20 cm⁻¹) and T¯ (16 cm⁻¹). Adiabatically cooled DPM was irradiated by a pair of femtosecond laser pulses (pumps) to excite modes T and T¯ through impulsive stimulated Raman scattering. Then, resonance two-photon ionization (R2PI) spectra were obtained by nanosecond UV pulses (∼268 nm, probe). Populations in v = 1 of both vibrational modes were evaluated from the integrated intensities of hot bands appearing in the R2PI spectra. The experimental results show that the populations in v = 1 of mode T and T¯ oscillate against the double pump interval as a result of the wave-packet interference (Figure). By utilizing the difference in these oscillation periods, mode selective excitation was realized (dashed lines). We also conducted semiclassical calculations, where molecular vibration is treated quantum mechanically while molecular rotation is simulated by classical trajectory calculation, to show a good match-up with the observed time-evolution of populations
State-distribution control of large amplitude vibration in substituted biphenyls with intense laser pulses
No full textMade available in DSpace on 2020-06-26T03:04:12Z (GMT). No. of bitstreams: 2
4425.pdf: 18464 bytes, checksum: 617353b6b5029678f249d43fd4f22567 (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
Previous issue date: 23With recent advances in ultrashort laser technology, many studies using intense nonresonant laser fields have been conducted to control vibrational or rotational wave packets. In particular, control of large-amplitude low-frequency vibration, {\it e.g.}, torsional motion, is important because such vibration may cause a substantial change in molecular structure. For instance, torsional motion of biphenyl has deserved much attention since chirality and physical property of the molecule depend on its torsional angle. In this study, we coherently excite torsional vibration of substituted biphenyl derivatives by the interaction with ultrashort laser fields and the resultant vibrational excitation is monitored by recording resonant two-photon ionization (R2PI) spectrum. We further adopt double-pulse excitation to control vibrational state distribution via wave-packet interference.
Adiabatically cooled molecular sample of 2-fluorobiphenyl is irradiated by the fundamental output from a fs Ti:Sapphire laser. This pump pulse induces vibrational excitation through impulsive Raman process. With an appropriate delay after the pump-pulse irradiation, the SS excitation spectrum of the molecules is recorded via R2PI with the doubled output of a nanosecond dye laser (280 nm). A progression with almost constant spacings appears in the R2PI spectrum without the pump pulse. It has been assigned to that of the torsional mode from vibrational ground state, {\it i.e.}, \mbox{{\it v} = 0} ({\it v} being the quantum number of the torsional mode in the electronic ground state).\footnote{H. S. Im and E. R. Bernstein, J. Chem. Phys. {\bf 88}, 7337 (1988).} When the pump pulse is introduced, the intensity of each band is reduced and new bands appear. These bands are assigned to the progression from {\it v} = 1. These observations indicate that impulsive Raman excitation of torsional vibration is realized. We also conduct a double-pump pulse experiment, where a pair of pulses are implemented for excitation. In this experiment, we succeeded in controlling the state distribution of torsional vibration by adjusting the time delay between the two pump pulses
SIX-DIMENSIONAL MODEL ANALYSIS AND INTERMOLECULAR VIBRATIONAL SPECTROSCOPY OF BENZENE-METHANE vdW COMPLEX
No full textThe benzene-methane complex is a prototypical model for CH/π interaction. The binding energyᵃ and UV spectraᵇ of this system have been reported and ab initio calculations were performedᶜ. However, full dimensional (6D) intermolecular potential energy surface (IPS) has not been evaluated because of difficulties caused by high dimensionality.
In order to reconstruct a full dimensional IPS in the benzene-methane system, stimulated emission pumping and wave-packet observation pertinent to the S₀ state were carried out. The latter was performed as a pump-probe experiment combining impulsive stimulated Raman excitation by femtosecond pulses with state-selective ionization by resonant two-photon ionization. A new 6D model potential analysis was also performed. Single-point energy calculations were performed at CCSD(T)/aug-cc-pVTZ level of theory for 525 different complex configurations, and calculated results were fitted by the new model potential. Observed intermolecular bands were assigned by comparing the theoretical prediction. Deviations of the prediction from the observation are well within 3 cm−¹, which verifies the utility of the present IPS for benzene-methane
State-distribution Control Of Large Amplitude Vibration In Substituted Biphenyls With Intense Laser Pulses
No full textWith recent advances in ultrashort laser technology, many studies using intense nonresonant laser fields have been conducted to control vibrational or rotational wave packets. In particular, control of large-amplitude low-frequency vibration is important because such vibration may cause a substantial change in molecular structure. For instance, torsional motion of biphenyl has deserved much attention since chirality and physical properties of the molecule depend on its torsional angle. In this study, we coherently excite torsional vibration of substituted biphenyl derivatives by the interaction with ultrashort laser fields and the resultant vibrational excitation is monitored by recording resonant two-photon ionization (R2PI) spectrum. We further adopt double-pulse excitation to control vibrational state distribution via wave-packet interference.
Adiabatically cooled molecular sample of 2-fluorobiphenyl is irradiated by the fundamental output from a fs Ti:Sapphire laser. This pump pulse induces vibrational excitation through impulsive Raman process. With an appropriate delay after the pump-pulse irradiation, the SS excitation spectrum of the molecules is recorded via R2PI with the doubled output of a nanosecond dye laser (280 nm). A progression with almost constant spacings appears in the R2PI spectrum without the pump pulse. It has been assigned to that of the torsional mode from vibrational ground state, {\it i.e.}, \mbox{{\it v} = 0} ({\it v} being the quantum number of the torsional mode in the electronic ground state).\footnote{H. S. Im and E. R. Bernstein, J. Chem. Phys. {\bf 88}, 7337 (1988).} When the pump pulse is introduced, the intensity of each band is reduced and new bands appear. These bands are assigned to the progression from {\it v} = 1. These observations indicate that impulsive Raman excitation of torsional vibration is realized. We also conduct a double-pump pulse experiment, where a pair of pulses are implemented for excitation. In this experiment, we succeeded in controlling the state distribution of torsional vibration by adjusting the time delay between the two pump pulses.Made available in DSpace on 2021-09-24T21:10:04Z (GMT). No. of bitstreams: 2
4895.pdf: 18430 bytes, checksum: dc693f00995e49258c67ac8e4b3d3b8d (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
Previous issue date: 2021-06-24Made available in DSpace on 2022-01-21T16:09:10Z (GMT). No. of bitstreams: 4
4895.pdf.txt: 2329 bytes, checksum: 19b3cda8dfcc72569aeb8ca488114514 (MD5)
license.txt: 4802 bytes, checksum: 58353f9dd6876860dd5221f3d7872a95 (MD5)
4895.pdf: 18430 bytes, checksum: dc693f00995e49258c67ac8e4b3d3b8d (MD5)
RH06_4895.pdf: 197727 bytes, checksum: a441878a820efb60ab28b8676f5ab628 (MD5)
Previous issue date: 2021-06-2
VIBRONIC SPECTRA OF BENZENE CLUSTERS REVISITED: II. THE TRIMER
No full textT. Iimori and Y. Ohshima, J. Chem. Phys. 114, 2867 (2001). W. Scherzer, O. Kratzschmar, H. L. Selzle, and E. W. Schlag, Z. Naturforsch. 47a, 1248 (1992). O. Engkvist, P. Hobza, H. L. Selzle, and E. W. Schlag, J. Chem. Phys. 110, 5758 (1999).Author Institution: Graduate School of Science, Kyoto University; Department of Chemistry, Graduate School of Science, Kyoto UniversityAs the second part of our recent reinvestigation on the electronic spectra of benzene we present the trimer vibronic system studied by two-color (2C) resonance enhanced two-photon ionization (R2PI) and UV-UV holeburing experiments. This band system is observed only in the dimer-ion channel even with 2C-R2PI because of extensive fragmentation after photoionization, and thus it has been incorrectly assigned to an isomeric form of the Detailed examination with mixed samples of and has revealed that the parent neutral has a single isomeric form for each isotopomer, with . This observation confirms the equivalency in three benzene sites, which is consistent with the most stable cyclic form predicted by a NEMO One of the intermolecular modes shows prominent Franck-Condon activity, implying a substantial conformational change via photoexcitation. Other details observed in the vibrionc spectra, e.g., exitonic splitting, will also be discussed
Pure Rotational Spectroscopy Of Rare Gas Dimers Based On Rotational Wave Packet Imaging
No full textWe report time-domain rotational spectroscopy of argon dimer and krypton dimer by implementing time-resolved Coulomb explosion imaging of rotational wave packets. The rotational wave packets are created in the dimers with a ultrashort laser pulse, and their spatiotemporal evolution is fully characterized by measuring angular distribution of the fragment ions. The pump-probe measurements have been carried out up to a delay time of 16 ns. The alignment parameters, derived from the observed images, exhibit periodic oscillation lasting for more than 15 ns. Pure rotational spectrum of Ar is obtained by Fourier transformation of the time traces of the alignment parameters. The frequency resolution in the spectrum is about 90 MHz, the highest ever achieved for Ar. The rotational constant and the centrifugal distortion constant are determined with much improved presision than the previous experimental results: \emph{B} = 1.72713(9) GHz and \emph{D} = 0.0310(5) MHz. The present B value does not match within the quoted experimental uncertainty with that from the VUV spectroscopy, so far accepted as an experimental reference to assess theories. Spectrum of the krypton dimer will be also reported
PURE ROTATIONAL SPECTRA OF RARE GAS- COMPLEXES
No full textY. Ohshima, Y. Sumiyoshi, and Y. Endo, 51st International Symposium on Molecular Spectroscopy, Paper WF05 (1996). A. Nowek and J. Leszczynski, {J. Chem. Phys}., \textbf{105}, 6388 (1996).Author Institution: Dept. of Pure and Applied Sciences, The University of Tokyo; Dept. of Chemistry, Kyoto UniversityIn addition to the rotational spectrum of Ar- reported , that of Kr- was observed for the first time by using a PDN-FTMW spectroscopy. The complex was produced in a supersonic jet by discharging a mixture containing , CO, and Kr diluted in Ar. Rotational transitions of mono-substituted species on Kr, H, C, and O were also observed, yielding a precise substitution structure of the complex, where however a large amplitude bending motion of the complex had to be considered. The determined Rg-H distances were explained for species by considering a charge induced dipole-charge interaction. Furthermore, for Ar-, the Ar-H distance and the vibrational frequencies of the van der Waals modes, which were extimated by the centrifugal distortion constant and an analysis of the large amplitude bending motion, were in good agreement with a recent {ab initio}
- …
