The Role of the nπ* 1Au State in the Photoabsorption and Relaxation of Pyrazine |
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| Authors: | Dr Chih‐Kai Lin Dr Yingli Niu Prof Chaoyuan Zhu Prof Zhigang Shuai Prof Sheng Hsien Lin |
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| Institution: | 1. Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010 (Taiwan), Fax: (+886)?3‐5723764;2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617 (Taiwan);3. Key Laboratory of Organic Optoelectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084 (P.R. China);4. Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (P.R. China) |
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| 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, 1Au, which is conventionally regarded dark due to the dipole‐forbidden 1Au←1Ag 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. |
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| Keywords: | absorption pyrazines quantum chemistry excited states vibronic coupling |
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