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Vibronic coupling and excited-state reaction dynamics of pyrazine in 1 1B2u (1ππ*) state by resonance Raman spectroscopy and CASSCF calculation


Xuming Zheng, Department of Chemistry and State Key Laboratory of ATMMT(MOE), Zhejiang Sci-Tech University, Hangzhou, China 310018. E-mail:

Wei-Hai Fang, Department of Chemistry, Beijing Normal University, Beijing, China. E-mail:


The photophysics and photochemistry of pyrazine (C4H4N2, D2h) after excitation to the S2 (1 1B2u, 1ππ*) electronic state were studied by using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The B-band resonance Raman spectra in cyclohexane solvent were obtained at 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of pyrazine in the S2 (1 1B2u, 1ππ*) state. Three electronic states 1 1B3u, 1 1B1g, and 1 1B2g were found to couple with the S2 (1 1B2u, 1ππ*) state. Two conical intersection (CI) points CI[S2(B2u)/S1(B3u)] and CI[S1/S0] and one transition state of the isomerization between pyrazine and pyrimidine were predicted to play important roles in the photochemistry of pyrazine. On the basis of the calculations, the mechanism of the photoisomerization reaction between pyrazine and pyrimidine has been proposed. Copyright © 2012 John Wiley & Sons, Ltd.