title: The role of the nπ* 1A(u) state in the photoabsorption and relaxation of pyrazine.
abstract: 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.
authors.affiliation: Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan. ethene@gate.sinica.edu.tw
authors.forename: Chih-Kai
authors.initials: CK
authors.lastname: Lin
authors.forename: Yingli
authors.initials: Y
authors.lastname: Niu
authors.forename: Chaoyuan
authors.initials: C
authors.lastname: Zhu
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Shuai
authors.forename: Sheng Hsien
authors.initials: SH
authors.lastname: Lin