Browsing by Author "Kanno, Manabu"

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Ab initio quantum dynamical analysis of ultrafast nonradiative transitions via conical intersections in pyrazine
(2015-01-01)
Kanno, Manabu
;
Ito, Yuta
;
Shimakura, Noriyuki
;
Koseki, Shiro
;
Kono, Hirohiko
We theoretically investigated the mechanism of ultrafast nonradiative transition through conical intersections in photoexcited pyrazine by ab initio quantum dynamical calculations. This work was motivated by the recent theoretical and experimental studies that presented conflicting results: the former is the on-the-fly semiclassical surface hopping calculation combined with the time-dependent density functional theory, which showed that nonadiabatic transitions from the optically bright S-2 (B-1(2u), pi pi*) state to the optically dark S-3 ((1)A(u), n pi*) and S-4 (B-1(2g), n pi*) states take place predominantly at the initial stage of electronic relaxation [U. Werner et al., Chem. Phys., 2008, 349, 319]; the latter is the pump-probe photoelectron spectroscopic measurement, which reported the S2 lifetime (22 +/- 3 fs) of nonradiative decay to the almost dark S-1 (B-1(3u), n pi*) state [Y.-I. Suzuki et al., J. Chem. Phys., 2010, 132, 174302]. We constructed adiabatic and diabatic potential energy surfaces of these pi pi* and n pi* states using the multireference configuration interaction method and calculated their diabatic couplings within two-dimensional subspaces spanned by selected ground-state normal coordinates. Contrary to the surface hopping study, our nuclear wave packet simulations demonstrated that nonadiabatic transitions to the S-3 and S-4 states are so small that the conventional two-state (S-1 and S-2) picture is valid. Ultrafast internal conversion of pyrazine, which is deemed to proceed with a 22 fs lifetime, in fact consists of three consecutive steps: (i) the wave packet excited to the S-2 state travels toward the S-2-S-1 conical intersection in 10 fs, (ii) the nonadiabatic transition to the S-1 state progresses at a rapid rate corresponding to a transient lifetime of 7 fs, and (iii) intramolecular vibrational energy redistribution occurs in the S-1 state in about 80 fs after optical excitation. To verify this prediction, time-resolved experiments with a resolution of several fs or shorter are desirable.
Ab Initio Quantum Dynamical Study on Ultrafast Nonradiative Transition Pathways of Pyrazine
(2015-01-01)
Kanno, Manabu
;
Ito, Yuta
;
Shimakura, Noriyuki
;
Koseki, Shiro
;
Kono, Hirohiko
We theoretically verified the participation of optically dark n pi* states other than S-1 in ultrafast internal conversion of pyrazine. Contrary to a recent semiclassical study, our quantum dynamical calculations demonstrated that their contributions are negligible.
Coherent ring currents in chiral aromatic molecules induced by linearly polarized UV laser pulses
(2013)
Kanno, Manabu
;
Kono, Hirohiko
;
Mineo, Hirobumi
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
Laser-Control of Ultrafast pi-Electron Ring Currents in Aromatic Molecules: Roles of Molecular Symmetry and Light Polarization
(2018-12-01)
Kanno, Manabu
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
;
Institute of Molecular science
Being motivated by the recent progress in attosecond laser technology, we theoretically explore the strategy of inducing ultrafast electron dynamics inherent to aromatic molecules, i.e., ring currents by means of polarized laser pulses. The main topic of discussion is how to control the direction of ring currents in an aromatic molecule of low symmetry, for which the design of an efficient control pulse cannot be achieved intuitively. We first consider a system with a single aromatic ring and show that coherent pi-electron angular momentum, which oscillates with time, can be produced and controlled by a polarized laser pulse with its ellipticity and orientation properly chosen. Nonadiabatic couplings with molecular vibration gradually weaken the angular momentum, while the vibrational amplitude strongly depends on the polarization of incident light. This suggests the conversion of the polarization dependence of ring current into that of subsequent vibration, which may open a way to detect laser-driven ultrafast electron dynamics by vibrational spectroscopy. The laser-control scheme for the ring current is then extended to a molecule with two aromatic rings, which exhibits characteristic phenomena absent in that with a single ring. We demonstrate that two-dimensional switching of the direction of angular momentum is possible in such molecules. In addition, ring current can be localized at a specific ring by tailored lasers. The application of the present control method to polycyclic aromatic hydrocarbons will lead to the development of next-generation organic optical switching devices.
Laser-Polarization Effects on Coherent Vibronic Excitation of Molecules with Quasi-Degenerate Electronic States
(2012-11-22)
Kanno, Manabu
;
Ono, Yukari
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
The laser-polarization effects on nonadiabatically couple pi-electron rotation (ring current) and molecular vibration have been theoretically analyzed for aromatic molecules with quasi-degenerate excited states irradiated by an ultrashort laser pulse of arbitrary polarization. We first derived general formulations of the coherent electronic wave packet and expectation value of electronic angular momentum within a frozen-nuclei model. The relative quantum phase of the superposed quasi-degenerate States, which.. determines the oscillating behavior of angular momentum; can be manipulated by the ellipticity and orientation of the incident laser. Nuclear wave packet simulations with a model molecule confirmed the controllability of pi-electron rotation, although the angular momentum is gradually reduced by nonadiabatic couplings. The amplitude of molecular vibration depends prominently on the orientation of linear polarization vectors rather than the helicity of circular polarization. The characteristic feature in vibrational amplitudes is attributed to the interference in nonadiabatic transition governed by the-relative quantum phase between nuclear wave packets. This offers a new strategy for laser control of molecular vibrations through the wave packet interference in nonadiabatic transition.
Nonadiabatic Response Model of Laser-Induced Ultrafast pi-Electron Rotations in Chiral Aromatic Molecules
(2010-03-12)
Kanno, Manabu
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
Lin, Sheng H.
;
應用化學系
We theoretically investigated the nonadiabatic couplings between optically induced pi-electron rotations and molecular vibrations in a chiral aromatic molecule irradiated by a nonhelical, linearly polarized laser pulse. The results of wave packet dynamics simulation show that the vibrational amplitudes strongly depend on the initial rotation direction, clockwise or counterclockwise, which is controlled by the polarization direction of the incident pulse. This suggests that attosecond pi-electron rotations can be observed by spectroscopic detection of femtosecond molecular vibrations.
Nonadiabatically Coupled pi-Electron Rotation and Molecular Vibration in Aromatic Molecules Excited by Polarized UV/Vis Laser Pulses
(2014-02-01)
Kanno, Manabu
;
Ono, Yukari
;
Kono, Hirohiko
;
Fujimura, Yuichi
;
應用化學系分子科學碩博班
We review our theoretical studies on laser-driven ultrafast pi-electron rotation (ring current) and vibronically coupled molecular vibrations in aromatic molecules with quasi-degenerate excited states. The main focus of discussion is on the role of laser polarization in controlling the coherent vibronic dynamics. We first present general formulations of the coherent electronic wave packet and expectation value of electronic angular momentum for arbitrary laser polarization within a frozen-nuclei model. We show that the relative quantum phase of the superposed quasi-degenerate states, which determines the oscillating behavior of angular momentum, can be manipulated by the ellipticity and orientation of the incident laser. The controllability of pi-electron rotation is demonstrated by electronic wave packet simulations for a model molecule. The results of nuclear wave packet simulations on effective potential energy surfaces of the molecule have revealed that the angular momentum is gradually reduced by nonadiabatic transitions. The amplitude of induced molecular vibration depends significantly on the direction of linear polarization vectors but is insensitive to the helicity of circular polarization. The characteristic feature in vibrational amplitudes is attributed to the interference between nuclear wave packets that acquire different quantum phases in nonadiabatic transition. This feature offers a new strategy for laser control of molecular vibrations through the wave packet interference in nonadiabatic transition.
Ultrafast nonradiative transition pathways in photo-excited pyrazine: Ab initio analysis of time-resolved vacuum ultraviolet photoelectron spectrum
(2018-11-14)
Mignolet, Benoit
;
Kanno, Manabu
;
Shimakura, Noriyuki
;
Koseki, Shiro
;
Remacle, Francoise
The internal conversion of photo-excited pyrazine, which occurs rapidly on a time scale of about 20 fs, has long been considered to proceed via a conical intersection between the optically bright S-2 (B-1(2u), pi pi*) and dark S-1 (B-1(3u), n pi*) states. Since 2008, several theoretical studies have raised the possibility that other dark states S-3 ((1)A(u), n pi*) and S-4 (B-1(2g), n pi*) may participate dominantly in the early stage of the nonradiative decay of S-2. To clarify this issue, being motivated by the recent pump-probe experiment by Horio et al. [J. Chem. Phys. 145 (2016) 044306], we calculated vacuum ultraviolet photoelectron spectra for ionization from each of the four excited states. Comparison was made with the measured time-resolved photoelectron spectrum exhibiting a temporally varying multi-band structure. We confirmed no contribution of S-3 or S-4 and thus the validity of the conventional two-state (S-2 -> S-1) picture for ultrafast nonradiative transition in pyrazine.