Isotope effects on vibronic coupling of pyrazine

Abstract

The vibronic couplings of pyrazine- d 0 and pyrazine- d 4 between the lowest electronic excited states 1B 3u(n, π ∗) and 1B 2u(π, π ∗) through the out-of-plane CH bending vibration ν 10 a ( b 1 g ) have been studied from the Raman, electronic absorption and fluorescence spectra. The isotope effects on the scattering cross section of the ν 10 a Raman line, the vibrational potential in the 1B 3u(n, π ∗) state and on the frequency change of the ν 10 a vibration between the ground and the lowest electronic excited states are well explained by conventional Herzberg-Teller coupling mechanism. However, the intensities of the vibronic bands in the electronic absorption and fluorescence spectra are hardly explained with this coupling mechanism.