This film illustrates some results from a study of HCl dissociation in molecular clusters. The calculations of the equilibrium structure are carried out by treating the proton quantum mechanically using Feynman's path integral representation of quantum mechanics; the remaining species are treated classically.
One aspect of the dissociation process in a cluster composed acetonitrile (CH3CN) molecules is shown. The H+ and Cl- ions are constrained to lie 27 angstroms apart. One sees in the film a series of configurations that contribute to the equilibrium structure. In particular, some configurations correspond to clusters of solvent molecules around each ion, while in other configurations one sees a "rubber band"-like structure where the solvent molecules form a bridge between the two ions. This leads to an attractive force binding the ions that is not found in bulk systems.
D. Laria, R. Kapral, D. Estrin, G. Ciccotti, "Acid Ionization in Polar Solvents: Cluster and Bulk Environments", to be published.