The role of the nπ* 1Au state in the photoabsorption and relaxation of pyrazine

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


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, 1Au, which is conventionally regarded dark due to the dipole-forbidden 1A u1Ag 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* 1B3u and ππ* 1B2u states through vibronic coupling. The scans on potential-energy surfaces further indicated that the 1Au state intersects with the 1B2u states near the equilibrium of the latter, thus implying its participation in the ultrafast relaxation process.

Original languageEnglish
Pages (from-to)2977-2985
Number of pages9
JournalChemistry - An Asian Journal
Issue number11
StatePublished - 4 Nov 2011


  • absorption
  • excited states
  • pyrazines
  • quantum chemistry
  • vibronic coupling


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