Microscopic friction and solvation in barrier crossing: isomerization of stilbene in size-selected hexane clusters

In order to understand the roles of bulk friction and solvation in barrier crossing reactions, here we report our first study of the isomerization rates for a beam of t-stilbene-hexanen clusters, n = 1–5, at excess energies covering the range Eex = 0–4000 cm−1. We observe that rates measured at excess energies well above the t-stilbene isomerization barrier decrease monotonically with increasing number of solvent molecules. The influence of microscopic solvation on the rates is systematically studied and related to changes in barrier height and internal friction, both key to the understanding of behavior in the bulk.