Radiationless transitions in systems with quasidiscrete spectrum

Radiationless electronic transitions in polyatomic molecules are studied assuming quasidiscrete vibrational spectra. As is shown, the existence of Fermi resonances in such systems allows one to understand irreversible radiationless transitions in isolated molecules. Applying this approach to a molecule in a condensed host material one manages to understand the causes of the early onset of the temperature dependence in the rate constant for radiationless transitions in a number of aromatic compounds.