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The Role of the nπ* 1 A u State in the Photoabsorption and Relaxation of Pyrazine
Author(s) -
Lin ChihKai,
Niu Yingli,
Zhu Chaoyuan,
Shuai Zhigang,
Lin Sheng Hsien
Publication year - 2011
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201100472
Subject(s) - pyrazine , excited state , atomic physics , singlet state , relaxation (psychology) , ground state , chemistry , dipole , absorption spectroscopy , absorption (acoustics) , vibronic coupling , spectral line , vibrational energy relaxation , physics , quantum mechanics , optics , psychology , social psychology , organic chemistry , stereochemistry
The geometric, energetic, and spectroscopic properties of the ground state and the lowest four singlet excited states of pyrazine have been studied by using DFT/TD‐DFT, CASSCF, CASPT2, and related quantum chemical calculations. The second singlet nπ* state, 1 A u , which is conventionally regarded dark due to the dipole‐forbidden 1 A u ← 1 A g transition, has been investigated in detail. Our new simulation has shown that the state could be visible in the absorption spectrum by intensity borrowing from neighboring nπ* 1 B 3u and ππ* 1 B 2u states through vibronic coupling . The scans on potential‐energy surfaces further indicated that the 1 A u state intersects with the 1 B 2u states near the equilibrium of the latter, thus implying its participation in the ultrafast relaxation process.