Browsing by Author "Yu, Jianguo"

Now showing 1 - 4 of 4

Anharmonic Franck-Condon simulation of the absorption and fluorescence spectra for the low-lying S-1 and S-2 excited states of pyrimidine
(2012-05-25)
Yang, Ling
;
Zhu, Chaoyuan
;
Yu, Jianguo
;
Lin, Sheng Hsien
;
應用化學系分子科學碩博班
Intensities and profiles of vibronic spectra of the low-lying singlet excited states were investigated with anharmonic and harmonic Franck-Condon simulations for pyrimidine. The first-order anharmonic correction shows dynamic shift of spectra that is exactly same as difference of reorganization energy between ground and excited states. The first-order correction show intensity enhancement of absorption and intensity weakening of fluorescence for S-1 state, and dynamic shift is also significant. On the other hand, the first-order correction is negligible for S-2 state. The main spectral progressions are well described by totally symmetry modes v(6a), v(1) and v(12). One mode from non-total symmetry v(16a) contributes to the weak band at 16a(2) transition for S-1 state. Four ab initio methods were employed in simulation; CASSCF, CASPT2, DFT and TD-DFT, and coupled-cluster singles-doubles (CCSD) and the equation-of-motion (EOM-CCSD) methods. They all work well, but CASSCF method show the best agreement with experiment for the weak-band intensities. (C) 2012 Elsevier B.V. All rights reserved.
Intersystem crossing-branched excited-state intramolecular proton transfer for o-nitrophenol: An ab initio on-the-fly nonadiabatic molecular dynamic simulation
(2016-05-25)
Xu, Chao
;
Yu, Le
;
Zhu, Chaoyuan
;
Yu, Jianguo
;
Cao, Zexing
The 6SA-CASSCF(10, 10)/6-31G (d, p) quantum chemistry method has been applied to perform on-the-fly trajectory surface hopping simulation with global switching algorithm and to explore excited-state intramolecular proton transfer reactions for the o-nitrophenol molecule within low-lying electronic singlet states (S-0 and S-1) and triplet states (T-1 and T-2). The decisive photoisomerization mechanisms of o-nitrophenol upon S-1 excitation are found by three intersystem crossings and one conical intersection between two triplet states, in which T-1 state plays an essential role. The present simulation shows branch ratios and timescales of three key processes via T-1 state, non-hydrogen transfer with ratio 48% and timescale 300 fs, the tunneling hydrogen transfer with ratios 36% and timescale 10 ps, and the direct hydrogen transfer with ratios 13% and timescale 40 fs. The present simulated timescales might be close to low limit of the recent experiment results.
Photoisomerization Reaction Mechanisms of o-Nitrophenol Revealed by Analyzing Intersystem Crossing Network at the MRCI Level
(2015-10-22)
Xu, Chao
;
Yu, Le
;
Zhu, Chaoyuan
;
Yu, Jianguo
;
應用化學系分子科學碩博班
6SA-CASSCF(10, 10) /6-31G (d, p) and MRCl/cc-pVDZ methods were performed to probe photoisomerization reaction mechanisms of o-nitrophenol. Two low-lying singlet electronic states (S-0 and S-1) and two low-lying triplet electronic states (T-1 and T-2) were found to weave an intersystem crossing network in which a dominant stepwise photoisomerization provides a very efficient reaction pathway; the reaction takes place in the wide region of crossing seam-surface woven by S-1 and T-1 states first, followed by T-1 and S-0 states. Both intersystem crossing regions show strong spin orbital coupling in the order of 40 wavenumbers. All nitro and aci-nitro isomers and transition states on four electronic potential energy surfaces are calculated along with analysis of both dominant and subdominant relaxation pathways, especially weak spin-orbital coupling (similar to 10 wavenumbers) between T-2 and S-1 states and effective conical intersection between T-2 and T-1 states opening a new relaxation pathway S-1 -> T-2 -> T-1.
Topology of conical/surface intersections among five low-lying electronic states of CO2: Multireference configuration interaction calculations
(2013-10-21)
Zhou, Bo
;
Zhu, Chaoyuan
;
Wen, Zhenyi
;
Jiang, Zhenyi
;
Yu, Jianguo
Multi-reference configuration interaction with single and double excitation method has been utilized to calculate the potential energy surfaces of the five low-lying electronic states (1)A(1), (1)A(2), (3)A(2), B-1(2), and B-3(2) of carbon dioxide molecule. Topology of intersections among these five states has been fully analyzed and is associated with double-well potential energy structure for every electronic state. The analytical potential energy surfaces based on the reproducing kernel Hilbert space method have been utilized for illustrating topology of surface crossings. Double surface seam lines between (1)A(1) and B-3(2) states have been found inside which the B-3(2) state is always lower in potential energy than the (1)A(1) state, and thus it leads to an angle bias collision dynamics. Several conical/surface intersections among these five low-lying states have been found to enrich dissociation pathways, and predissociation can even prefer bent-geometry channels. Especially, the dissociation of O(P-3) + CO can take place through the intersection between B-3(2) and B-1(2) states, and the intersection between (3)A(2) and B-1(2) states. c 2013 AIP Publishing LLC.