The role of the nπ* 1A(u) state in the photoabsorption and relaxation of pyrazine

Chih-Kai Lin; Yingli Niu; Chaoyuan Zhu; Zhigang Shuai; Sheng Hsien Lin

doi:10.1002/asia.201100472

The role of the nπ* 1A(u) state in the photoabsorption and relaxation of pyrazine

Chem Asian J. 2011 Nov 4;6(11):2977-85. doi: 10.1002/asia.201100472. Epub 2011 Sep 16.

Authors

Chih-Kai Lin¹, Yingli Niu, Chaoyuan Zhu, Zhigang Shuai, Sheng Hsien Lin

Affiliation

¹ Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan. ethene@gate.sinica.edu.tw

PMID: 21922672
DOI: 10.1002/asia.201100472

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.