Electronic spectra and vibronic coupling of pyrazine

Abstract

The absorption and fluorescence spectra of pyrazine have been observed in vapor, solution and crystal, and the vibrational structures have been analyzed in detail. The fluorescence spectrum consists of long progressions of the nontotally symmetric vibration ν 5( b 2 g ), and the absorption spectrum contains also the progression of the corresponding excited state vibration ν′ 5( b 2 g . However, the pattern of the latter progression is unusual because of the highly anharmonic nature of the potential of the 1 B 3 u state, which may be expressed by a functional form containing a quadratic term in the normal coordinate. All the experimental results suggest that the known vibronic interaction between the 1B 3u(n,π ∗) state and the 1B 1u(π, π ∗) state through the vibration ν 2( b 2 g ) is strong. The vibronic coupling and the potential of the 1 B 3 u state were found to be very sensitive to solvent.