Browsing by Author "Fujimura, Y."

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Adiabatic treatment for vibrational predissociation of water dimers with channel interactions
(2015-01-01)
Mineo, H.
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Lin, S. H.
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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.
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.
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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]
Density Functional Theory Study of Conformation-Dependent Properties of Neutral and Radical Cationic L-Tyrosine and L-Tryptophan
(2011-09-01)
Baek, K. Y.
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Fujimura, Y.
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Hayashi, M.
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Lin, S. H.
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Kim, S. K.
Conformation-dependent properties of L-tyrosine and L-tryptophan in neutral and radical cations were studied by using the density functional theory (DFT) with a new density functional M05-2X. The results are compared with those obtained by using the conventional DFT (B3LYP). Results obtained by both types of DFT were in qualitative accord, including the existence of two conformational subgroups and their subgroup-dependent adiabatic ionization energy and hydrogen bonding. On the other hand, quantitative differences were found between the two DFT methods as well: the M05-2X method successfully reproduced experimental adiabatic ionization energy, whereas the B3LYP functional consistently yielded significantly lower values by 0.2-0.3 eV. More importantly, natural bond orbital (NBO) analysis for cationic conformers showed that all conformers of L-tyrosine and L-tryptophan undergo charge localization upon ionization regardless of the presence of intramolecular hydrogen bonding, unlike the case of L-phenylalanine that was treated earlier by other studies. Different degrees of charge localization among all three aromatic amino acids are explained by employing a simple model in which the aromatic amino acid is assumed to consist of two submoieties of distinct cationic core: the backbone and aromatic side chain. The difference in adiabatic ionization energy between these two submoieties is found to govern the degree of charge localization.
Investigation of Conformation-Dependent Properties of L-Phenylalanine in Neutral and Radical Cations by Using a Density Functional Taking into Account Noncovalent Interactions
(2010-07-22)
Baek, K. Y.
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Hayashi, M.
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Fujimura, Y.
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Lin, S. H.
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Kim, S. K.
Conformation-dependent properties of L-phenylalanine in neutral and radical cations have been studied by using density functional theory (DFT) with a new density functional M05-2X, which is applicable to molecular systems with nonconvalent interactions. Adiabatic and vertical ionization energies and charge distributions in the cationic conformers in addition to optimized geometrical structures for both the neutral and the cationic conformers were evaluated. These results were compared with DFT (B3LYP) results. The M05-2X results can explain the correspondence between the observed and predicted conformers without ambiguity. The possibility of conformerization of neutral conformers is indicated from the results of IRC (intrinsic reaction coordinate) profiles.
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 chemical calculation of intramolecular vibrational redistribution and vibrational energy transfer of water clusters
(2013-10-24)
Niu, Y. L.
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Pang, R.
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Zhu, C. Y.
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Hayashi, M.
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Fujimura, Y.
In present letter the adiabatic approximation is applied to the intramolecular vibrational redistribution (IVR) of water clusters. The isotope, blocking and cluster-size effects are investigated. This letter also examines the assumption associated with the transition state theory applied to unimolecular reactions; that is, IVR is assumed to be completed before the reaction takes place. For this purpose, we choose to study (H2O)(2)H+ -> H2O+ H3O+, and (H2O)(2) -> 2H(2)O processes. In molecular clusters, the vibrational excitation energy transfer between different normal modes has been observed. This will also be investigated for the deuterated species of (HOD)(2)H+. (C) 2013 Elsevier B.V. All rights reserved.
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.
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).
Theory and Applications of Sum-Frequency Generations
(2014-01-01)
Lin, C. K.
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Yang, L.
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Hayashi, M.
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Zhu, C. Y.
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Fujimura, Y.
The SFG technique has become popular since the pioneering work conducted by Shen's group in late 1980s. Combined the advantages of other surface-detecting techniques, the SFG technique could identify both chemical species and orientations adsorbed on surfaces or inserted between surfaces. In view of the recent tremendous experimental activities of SFG in surface chemistry, biochemistry and material sciences, quantum chemical calculations of SFG spectra to analyze the experimental SFG spectra are badly needed. In this paper we presented the theoretical expressions of various SFG techniques and showed how to employ the quantum chemical calculations to simulate the corresponding SFG spectra.
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.
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.