Knowledge Bank

Molecular dynamics simulations of $SF6.(Rg)n$ clusters $(n=5-12)$, where $Rg=Ar$ and Kr, have been used to determine the minimum energy structures and study dynamical properties, such as transitions between liquid- and solid-like structures. A model, developed by Eichenauer and $LeRoy,1$ which predicts the frequency shifts of the $\nu 3$ band of the infrared-active $SF6$ chromophore, has been used to characterize these clusters. The magnitude of the frequency shift has proved to be a sensitive probe of the distinct catchment regions'' on the potential energy surface which are accessed in the course of a trajectory. Abrupt changes in the frequency shift have been found to be associated with spontaneous iso-energetic isomerizations between structures consisting of a liquid-like monolayer of Ar atoms coating the $SF_{6}$, and others in which a solid-like cap'' of (Ar)n forms on one face of the $SF6$ molecule. It has been observed that ``melting'' is accompanied by a broadening of the simulated $\nu 3$ band, behaviour similar to that observed experimentally by Hahn and $Whetten2$ in studies of a benzene chromophore in Ar clusters, Illustrative examples of the use of the infrared-active $\nu 3$ band of the $SF6$ chromophore in probing the structure and dynamical properties of some impure rare gas clusters will be presented and discussed.