Browsing by Author "Mineo, H."

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A master equation approach to the dynamics of zero electron kinetic energy (ZEKE) states and ZEKE spectroscopy
(2011-02-14)
Wang, Yi-Hsieh
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Mineo, H.
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Chao, S. D.
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Selzle, H. L.
;
Neusser, H. J.
We have theoretically studied important dynamic processes involved in zero electron kinetic energy (ZEKE) spectroscopy using the density matrix method with the inverse Born-Oppenheimer approximation basis sets. In ZEKE spectroscopy, the ZEKE Rydberg states are populated by laser excitation (either a one- or two- photon process), which is followed by autoionizations and l-mixing due to a stray field. The discrimination field is then applied to ionize loosely bound electrons in the ZEKE states. This is followed by using the extraction field to extract electrons from the ZEKE levels which have a strength comparable to that of the extraction field. These extracted electrons are measured for the relative intensities of the ion states under investigation. The spectral positions are determined by the applied laser wavelength and modified by the extraction electric field. In this paper, all of these processes are conducted within the context of the density matrix method. The density matrix method can provide not only the dynamics of system's population and coherence (or phase) but also the rate constants of the processes involved in the ZEKE spectroscopy. Numerical examples are given to demonstrate the theoretical treatments. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3547363]
Adiabatic treatment for vibrational predissociation of water dimers with channel interactions
(2015-01-01)
Mineo, H.
;
Lin, S. H.
;
Fujimura, Y.
;
應用化學系
;
應用化學系分子科學碩博班
The results of calculated vibrational predissociation (VPD) of water dimers are presented. The VPD processes considered here are the followings: initially closed channel of symmetric stretching mode is excited by one quantum, and dissociate to two open channels of the bending mode excitation by one quantum in the donor and acceptor units. The VPD rate constants are calculated in the quantum mechanical approach under the adiabatic approximation. The channel interactions were taken into account in and between the initial and final states. The results obtained by quantum-mechanical approach are compared with both experimental and semi-classical trajectory calculation results.
Autoionization rate constants of zero electron kinetic energy Rydberg states
(2012-03-13)
Mineo, H.
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Wang, Y. H.
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Chao, S. D.
;
Lin, S. H.
;
應用化學系
We have calculated the vibrational and rotational autoionization rate constants for diatomic molecules H-2, N-2, and HCl in high Rydberg states by employing the density matrix formulation with the inverse Born-Oppenheimer approximation basis set. The purpose is to simulate the main radiationless processes occurring in zero electron kinetic energy (ZEKE) spectroscopy. The quantum numbers and the energy dependences of the calculated autoionization rate constants are represented as the scaling laws via nonlinear regression. These data provide a suitable starting point for quantitative study of the intricate dynamics involved in ZEKE Rydberg states. (C) 2012 Elsevier B. V. All rights reserved.
Coherent pi-electron dynamics of (P)-2,2 '-biphenol induced by ultrashort linearly polarized UV pulses: Angular momentum and ring current
(2013-02-21)
Mineo, H.
;
Lin, S. H.
;
Fujimura, Y.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The results of a theoretical investigation of coherent pi-electron dynamics for nonplanar (P)-2,2'-biphenol induced by ultrashort linearly polarized UV pulses are presented. Expressions for the time-dependent coherent angular momentum and ring current are derived by using the density matrix method. The time dependence of these coherences is determined by the off-diagonal density matrix element, which can be obtained by solving the coupled equations of motion of the electronic-state density matrix. Dephasing effects on coherent angular momentum and ring current are taken into account within the Markov approximation. The magnitudes of the electronic angular momentum and current are expressed as the sum of expectation values of the corresponding operators in the two phenol rings (L and R rings). Here, L (R) denotes the phenol ring in the left (right)-hand side of (P)-2,2'-biphenol. We define the bond current between the nearest neighbor carbon atoms C-i and C-j as an electric current through a half plane perpendicular to the C-i-C-j bond. The bond current can be expressed in terms of the inter-atomic bond current. The inter-atomic bond current (bond current) depends on the position of the half plane on the bond and has the maximum value at the center. The coherent ring current in each ring is defined by averaging over the bond currents. Since (P)-2,2'-biphenol is nonplanar, the resultant angular momentum is not one-dimensional. Simulations of the time-dependent coherent angular momentum and ring current of (P)-2,2'-biphenol excited by ultrashort linearly polarized UV pulses are carried out using the molecular parameters obtained by the time-dependent density functional theory (TD-DFT) method. Oscillatory behaviors in the time-dependent angular momentum (ring current), which can be called angular momentum (ring current) quantum beats, are classified by the symmetry of the coherent state, symmetric or antisymmetric. The bond current of the bridge bond linking the L and R rings is zero for the symmetric coherent state, while it is nonzero for the antisymmetric coherent state. The magnitudes of ring current and ring current-induced magnetic field are also evaluated, and their possibility as a control parameter in ultrafast switching devices is discussed. The present results give a detailed description of the theoretical treatment reported in our previous paper [H. Mineo, M. Yamaki, Y. Teranish, M. Hayashi, S. H. Lin, and Y. Fujimura, J. Am. Chem. Soc. 134, 14279 (2012)]. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790595]
Experimental and theoretical investigation of high-power laser ionization and dissociation of methane
(2007-09-27)
Sharifi, A.
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Kong, F.
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Chin, S. L.
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Mineo, H.
;
Dyakov, Y.
The main purpose of this paper is to report the high-power laser ionization-dissociation of CH4 at various femtosecond (fs) laser intensities (from 1 x 10 14 W/cm(2) to 2 x 1015 W/cm(2)) with a laser pulse duration of 48 fs. The generalized molecular Keldysh theory has been applied to calculate the ionization yields for CH4+ and CH4++. Outside the influence of the A intense laser, we propose to calculate the mass spectra due to the decomposition of CH4+ and CH4++, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The agreement between the experimental mass spectra and calculated mass spectra seems to be reasonable.
Experimental and theoretical investigations of ionization/dissociation of cyclopentanone molecule in a femtosecond laser field
(2008-11-28)
Wang, Qiaoqiao
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Wu, Di
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Jin, Mingxing
;
Liu, Fuchun
;
Hu, Feifei
The ionization/dissociation mechanism of cyclopentanone has been experimentally investigated in molecular beam by irradiating with intense 394 and 788 nm laser fields with pulse duration of 90 fs. The range of laser intensities varied from 3 X 10(13) to 4 X 10(14) W/cm(2). For both wavelengths, the singly charged parent ion is observable while the doubly charged one cannot be found easily, although the fragmentation pattern supports its presence. Meanwhile, the extent of fragmentation at 788 nm is less than that in the 394 nm case. We quantitatively analyze the ionization processes of cyclopentanone in intense femtosecond laser by comparing the calculation results of ionization rate constants obtained from Ammosov-Delone-Krainov, Keldysh, and Keldysh-Faisal-Reiss (KFR) theories based on hydrogenlike atom model. We also compare the experimental and theoretical results; the generalized KFR theory is found to be useful in predicting the ionization yields of singly and doubly charged cyclopentanone ion. To interpret the dissociation patterns of the cyclopentanone ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations. (c) 2008 American Institute of Physics.
Highly Multiphoton Excitation of Molecule by Intense Laser Field
(2009)
Teranishi, Y.
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Hayashi, M.
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Song, D.
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Azarm, A.
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Kong, F.
Multiphoton excitation of molecule by intense laser field is studied theoretically to explain the recent experiments of neutral fragmentation Neutral fragments are created from highly excited parent molecule Excitation mechanism is discussed with the use of Floqet theory.
Highly multiphoton molecular excitation by an intense laser pulse
(2008)
Teranishi, Y.
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Hayashi, M.
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Kong, F.
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Chin, S. L.
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Chao, S. D.
Multiphoton excitation of molecules by an intense laser field is treated. When the first excitation energy is much larger than both the photon energy and the transition energy between excited states, excited states are strongly coupled with each other by the photon, even though coupling with the ground state is weak. In such a case, a kind of collective excitation takes places, in which the excitation probability of every excited state is almost linear as functions of intensity on a log-log plot, and the slope is independent of the final state. By taking methane and formaldehyde as examples we numerically study this process.
Molecular ionization of cyclohexanone in femtosecond laser fields: An application of ADK theory
(2009-08-01)
Wang, Q. Q.
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Mineo, H.
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Wu, D.
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Jin, M. X.
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Chin, C. H.
The mechanisms of ionization and dissociation of cyclohexanone (C(6)H(10)O) in a 90 fs, 788 nm linearly polarized laser field ranging from 10(13) to 10(14) W/cm(2) by a time-of-flight mass spectrometer (TOF-MS) have been investigated. The ion yields as a function of laser intensity have been measured experimentally. By comparison with the Ammosov-Delone-Krainov (ADK) theory based on a hydrogen-like model, the ionization mechanism of cyclohexanone in this intense femtosecond laser field has been understood. Considering the importance of molecular nuclear motions, we propose that the Franck-Condon (F-C) factor can provide the excess vibrational energy in the molecular ion. This energy is required for the decomposition of the molecular ion which finally results in the observed mass spectrum.
Non-Markovian response of ultrafast coherent electronic ring currents in chiral aromatic molecules in a condensed phase
(2013-12-07)
Mineo, H.
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Lin, S. H.
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Fujimura, Y.
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Xu, J.
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Xu, R. X.
Results of a theoretical study on non-Markov response for femtosecond laser-driven coherent ring currents in chiral aromatic molecules embedded in a condensed phase are presented. Coherent ring currents are generated by coherent excitation of a pair of quasi-degenerated pi-electronic excited states. The coherent electronic dynamical behaviors are strongly influenced by interactions between the electronic system and phonon bath in a condensed phase. Here, the bath correlation time is not instantaneous but should be taken to be a finite time in ultrashort time-resolved experiments. In such a case, Markov approximation breaks down. A hierarchical master equation approach for an improved semiclassical Drude dissipation model was adopted to examine the non-Markov effects on ultrafast coherent electronic ring currents of (P)-2,2'-biphenol in a condensed phase. Time evolution of the coherent ring current derived in the hierarchical master equation approach was calculated and compared with those in the Drude model in the Markov approximation and in the static limit. The results show how non-Markovian behaviors in quantum beat signals of ring currents depend on the Drude bath damping constant. Effects of temperatures on ultrafast coherent electronic ring currents are also clarified. (C) 2013 AIP Publishing LLC.
Quantum-mechanical approach to predissociation of water dimers in the vibrational adiabatic representation: Importance of channel interactions
(2015-08-28)
Mineo, H.
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Niu, Y. L.
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Kuo, J. L.
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Lin, S. H.
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Fujimura, Y.
The results of application of the quantum-mechanical adiabatic theory to vibrational predissociation (VPD) of water dimers, (H2O)(2) and (D2O)(2), are presented. We consider the VPD processes including the totally symmetric OH mode of the dimer and the bending mode of the fragment. The VPD in the adiabatic representation is induced by breakdown of the vibrational adiabatic approximation, and two types of nonadiabatic coupling matrix elements are involved: one provides the VPD induced by the low-frequency dissociation mode and the other provides the VPD through channel interactions induced by the low-frequency modes. The VPD rate constants were calculated using the Fermi golden rule expression. A closed form for the nonadiabatic transition matrix element between the discrete and continuum states was derived in the Morse potential model. All of the parameters used were obtained from the potential surfaces of the water dimers, which were calculated by the density functional theory procedures. The VPD rate constants for the two processes were calculated in the non-Condon scheme beyond the so-called Condon approximation. The channel interactions in and between the initial and final states were taken into account, and those are found to increase the VPD rates by 3(1) orders of magnitude for the VPD processes in (H2O)(2) ((D2O)(2)). The fraction of the bending-excited donor fragments is larger than that of the bending-excited acceptor fragments. The results obtained by quantum-mechanical approach are compared with both experimental and quasi-classical trajectory calculation results. (C) 2015 AIP Publishing LLC.
Structure and predissociation of the 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2): First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis
(2008-11-28)
Wang, Qiaoqiao
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Wu, Di
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Jin, Mingxing
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Liu, Fuchun
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Hu, Feifei
The 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2) is studied experimentally using two high-resolution spectroscopic techniques. First, the forbidden D (3)Sigma(+)(u)-X (1)Sigma(+)(g) transition is observed for the first time via the (0,0) band of (14)N(2) and the (1,0) band of (15)N(2), using 1 extreme-ultraviolet +1 ultraviolet two-photon-ionization laser spectroscopy. Second, the Rydberg-Rydberg transition D (3)Sigma(+)(u)-E (3)Sigma(+)(g) is studied using near-infrared diode-laser photoabsorption spectroscopy, thus extending the previous measurements of Kanamori [J. Chem. Phys. 95, 80 (1991)], to higher transition energies, and thereby revealing the (2,2) and (3,3) bands. The combined results show that the D(v=0-3) levels exhibit rapidly increasing rotational predissociation as v increases, spanning nearly four orders of magnitude. The D-state level structure and rotational predissociation signature are explained by means of a coupled-channels model which considers the electrostatically coupled (3)Pi(u) Rydberg-valence manifold, together with a pure-precession L-uncoupling rotational interaction between the 3p sigma(u)D (3)Sigma(+)(u) and 3p pi(u)G (3)Pi(u) Rydberg p-complex components.
Structure and predissociation of the 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2): First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis
(2008-11-28)
Wang, Qiaoqiao
;
Wu, Di
;
Jin, Mingxing
;
Liu, Fuchun
;
Hu, Feifei
The 3p sigma(u)D (3)Sigma(+)(u) Rydberg state of N(2) is studied experimentally using two high-resolution spectroscopic techniques. First, the forbidden D (3)Sigma(+)(u)-X (1)Sigma(+)(g) transition is observed for the first time via the (0,0) band of (14)N(2) and the (1,0) band of (15)N(2), using 1 extreme-ultraviolet +1 ultraviolet two-photon-ionization laser spectroscopy. Second, the Rydberg-Rydberg transition D (3)Sigma(+)(u)-E (3)Sigma(+)(g) is studied using near-infrared diode-laser photoabsorption spectroscopy, thus extending the previous measurements of Kanamori [J. Chem. Phys. 95, 80 (1991)], to higher transition energies, and thereby revealing the (2,2) and (3,3) bands. The combined results show that the D(v=0-3) levels exhibit rapidly increasing rotational predissociation as v increases, spanning nearly four orders of magnitude. The D-state level structure and rotational predissociation signature are explained by means of a coupled-channels model which considers the electrostatically coupled (3)Pi(u) Rydberg-valence manifold, together with a pure-precession L-uncoupling rotational interaction between the 3p sigma(u)D (3)Sigma(+)(u) and 3p pi(u)G (3)Pi(u) Rydberg p-complex components.
Theoretical and Experimental Investigations of Ionization-Dissociation of Polyatomic Molecules
(2009)
Wang, Qiaoqiao
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Jin, Mingxing
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Ding, Dajun
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Mineo, H.
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Chao, S. D.
The Keldysh theory originally developed for the ionization of Is state of hydrogen atom has been generalized for molecules by introducing the molecular orbital theory and the Born-Oppenheimer approximation. Ionization and dissociation mechanisms of cyclopentanone in the intense 800 nm laser field (10(13) to 10(14) W/cm(2)) have been experimentally investigated by using a method of molecular beam and time-of-flight mass spectrometer (TOF-MS). Singly-charged parent ion and numerous fragment ions are observed in the mass spectra, which are analyzed by using the molecular Keldysh theory.
Theoretical studies of ZEKE spectroscopy and dynamics of high Rydberg states
(2010-02-12)
Wang, Yi-Hsieh
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Teranishi, Y.
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Mineo, H.
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Chao, S. D.
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Selzle, H. L.
A main purpose of this Letter is to show how to employ the inverse Born-Oppenheimer approximation as a basis set to study zero kinetic energy (ZEKE) spectroscopy and the autoionization dynamics of the ZEKE states. The calculations of channel couplings, quantum defects, intensity borrowing, vibrational and rotational autotionizations will be demonstrated by using a homonuclear diatomic molecule as an example. (C) 2010 Elsevier B. V. All rights reserved.
Theoretical Study of Coherent pi-Electron Rotations in a Nonplanar Chiral Aromatic Molecule Induced by Ultrafast Linearly Polarized UV Pulses
(2015-01-01)
Mineo, H.
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Fujimura, Y.
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應用化學系分子科學碩博班
;
Institute of Molecular science
We present the results of a theoretical study of pi-electron dynamics in a nonplanar chiral aromatic molecule (P)-2,2\'-biphenol. Coherent ring currents, which are one of the main observables of coherent pi-electron dynamics, are generated by applying the linearly polarized UV pulse laser, where a pair of coherent quasi-degenerated excited states is created. In this paper we review the formulations of the time-dependent coherent ring currents and angular momentum which were obtained using the density matrix theory based on the LCAO MO approximation. The results of the numerical simulation of coherent pi-electron ring currents and angular momentum in (P)-2,2\'-biphenol are shown. We also propose an ultrafast quantum switching method of pi-electron rotations and perform the sequential switching among four rotational patterns which are performed by the overlapped pump-dump laser pulses with properly selected laser polarizations, time delay and relative phases. Finally we refer to an outline for the extension of our method to N aromatic rings chain (N >= 3).
Ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate excited states in molecules: Population and vibrational coherence transfers
(2012-01-02)
Mineo, H.
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Kanno, M.
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Kono, H.
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Chao, S. D.
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Lin, S. H.
Results of a theoretical study of ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate pi-electronic excited states of molecules were presented. Analytical expressions for temporal behaviors of population and vibrational coherence were derived using a simplified model to clarify the quantum mechanical interferences between the two coherently excited electronic states, which appeared in the nuclear wavepacket simulations [M. Kanno, H. Kono, Y. Fujimura, S. H. Lin, Phys. Rev. Lett 104 (2010) 108302]. The photon-polarization direction of the linearly polarized laser, which controls the populations of the two quasi-degenerate electronic states, determines constructive or destructive interference. Features of the vibrational coherence transfer between the two coupled quasi-electronic states through nonadiabatic couplings are also presented. Information on both the transition frequency and nonadiabatic coupling matrix element between the two states can be obtained by analyzing signals of two kinds of quantum beats before and after transfer through nonadiabatic coupling. (C) 2011 Elsevier B. V. All rights reserved.
Ultrafast electronic motion in hydrogen molecular ions induced by a high power intense laser
(2010-10-20)
Mineo, H.
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Teranishi, Y.
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Chao, S. D.
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Lin, S. H.
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應用化學系分子科學碩博班
In this Letter we report a method for controlling electronic localization in a molecular ion, on an attosecond time scale, using a high-intensity laser, based on two different excitation mechanisms. One takes place during ionization, and the other takes place sequentially, following ionization. The electronic excited states of the hydrogen molecular ion are created during ionization by taking the configuration interaction mixing of neutral molecules into account. We detect the ultrafast oscillatory electronic motion between two atoms in a hydrogen molecular ion occurring due to the creation of excited states during the course of ionization. (c) 2010 Elsevier B.V. All rights reserved.
Ultrafast electronic motion in hydrogen molecular ions induced by a high power intense laser
(2010-10-20)
Mineo, H.
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Teranishi, Y.
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Chao, S. D.
;
Lin, S. H.
;
應用化學系
In this Letter we report a method for controlling electronic localization in a molecular ion, on an attosecond time scale, using a high-intensity laser, based on two different excitation mechanisms. One takes place during ionization, and the other takes place sequentially, following ionization. The electronic excited states of the hydrogen molecular ion are created during ionization by taking the configuration interaction mixing of neutral molecules into account. We detect the ultrafast oscillatory electronic motion between two atoms in a hydrogen molecular ion occurring due to the creation of excited states during the course of ionization. (c) 2010 Elsevier B.V. All rights reserved.
Vibrational effects on UV/Vis laser-driven pi-electron ring currents in aromatic ring molecules
(2014-10-17)
Mineo, H.
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Lin, S. H.
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Fujimura, Y.
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應用化學系分子科學碩博班
;
Institute of Molecular science
We present the results of a theoretical study of vibrational effects on UV/Vis laser-driven p-electron ring currents in aromatic ring molecules. We consider vibrational effects on both coherent and non-coherent (single quantum state) ring currents. The coherent ring current originates from an excitation of a pair of quasi-degenerate electronic states by an ultrashort linearly polarized UV/Vis laser pulse, while the non-coherent ring current originates from by an excitation of a degenerated electronic state of an aromatic ring molecule with high symmetry by a circularly polarized electric field of a UV/Vis laser pulse. The magnitude of a generated ring current can be expressed as an average of those of the bond currents for both the coherent and non-coherent cases. We derive an analytical expression for the magnitude of the bond currents in the adiabatic approximation. Using the expression, we performed calculations of a non-coherent ring current generated in the optically allowed excited state (E-1(1U)) of benzene and the time evolution of coherent ring current of (P)-2,2-biphenol. Vibrational effects on the non-coherent ring current of benzene were found to be negligibly small. We paid particular attention to the vibrational effects induced by the torsion mode on time evolution of the coherent ring current along the bond bridging between the two aromatic rings of (P)-2,2-biphenol. By comparing the time evolution of the coherent ring current with that in the frozen-nuclear approximation, we found that inclusion of the low-frequency torsion mode brings about modulations in the beating in the ring current. The modulations in the time evolution of the coherent ring current were brought about by contribution of several pairs of the coherently excited vibronic states. Coherent vibronic ring currents generated from pairs of the coherently excited vibronic states interfere each other. The existence of the pairs originates from relatively large potential displacement of the torsion mode between the two excited states for (P)-2,2-biphenol. Temperature effects on the time-dependent coherent ring current were also investigated. (C) 2014 Elsevier B.V. All rights reserved.