Beats in internal vibrational energy redistribution in trans-stilbene - A study of the quantum and classical correspondence

Starting from recently observed beating patterns in trans-stilbene we consider the correspondence of classical molecular dynamics and quantum dynamics for the description of the internal vibrational energy redistribution in molecules. The beat frequency of two modes in 2:1 resonance is investigated with respect to quantum effects, sensitivity to anharmonic coupling and indirect coupling via a third oscillator. We find a robust correspondence between classical and quantum beat frequencies but a large sensitivity to the coupling terms in the potential. Refined anharmonic coupling appears to be needed to resolve the very low frequency beating patterns observed in trans-stilbene.