The impact of a solvent and a methyl rotor on timescales of intramolecular vibrational energy redistribution in aromatic molecules

Abstract

Selectively excited benzene and toluene in the gas and solution phase have been investigated with ultrafast transient absorption spectroscopy to study the impact of a solvent on the time scales of intramolecular vibrational energy redistribution (IVR). It has been found that multiple time scales exist for isolated benzene (toluene) in agreement with theory. A comparison of gas-phase and solution experiments revealed the effect and magnitude of solvent assisted IVR. Although the ultrafast IVR component is hardly influenced by the solvent, the picosecond time scale of IVR appears to be contracted in solution with respect to the gas phase due to interactions (collisions) with the solvent and an overall acceleration of slower IVR components. In addition, we find that an internal rotor (i.e., a methyl group on an aromatic ring) accelerates IVR in the gas phase significantly whereas the effect appears to be largely concealed in solution.