Intramolecular Vibrational Redistribution at Low State Densities in S₁ Aromatics. Evidence for Rotational Contributions

Abstract

Evidence is presented concerning the onset of intramolecular vibrational redistribution (IVR) as one climbs the vibrational manifold of room temperature S₁ aromatics. The onsets of IVR occur at S₁ vibrational energies between 670 and 2000 cm⁻¹ for various single and double ring aromatic molecules. The vibrational level densities in the onset region seem too small to support the extensive IVR that is observed in every molecule. Comparisons of room temperature fluorescence spectra with cold supersonic beam spectra from p-difluorobenzene support the proposition that Coriolis vibration–rotation coupling makes important contributions to the effective density of states in room temperature IVR.