Single vibronic level fluorescence from 1B3u pyrazine: The role of Fermi resonance and Duschinski rotation

Abstract
We report a study of the 1B3u1Ag transition in pyrazine based on a combination of gas phase absorption and single vibronic level fluorescence spectra. Particular attention is paid to relative transition moments, especially where asymmetries exist between the intensities in the absorption and emission spectra. Band intensities and positions provide evidence for Fermi resonances and Duschinski rotations, but not for a symmetry change between the 1Ag and 1B3u states. Upper limits for displacements along several non‐totally symmetric normal coordinates are set, and a few new vibrational assignments are made.