STRUCTURE AND DYNAMICS OF MOLECULAR CLUSTERS .3. MONTE-CARLO STUDIES OF SMALL CLUSTERS OF TEF6

Melting and freezing transitions of clusters of tellurium hexafluoride containing 12, 13, and 14 molecules have been investigated using a seven-site intermolecular interaction potential. Various diagnostic methods were applied to simulations of heating and cooling stages including caloric curves, the Lindemann delta index, Pawley-Fuchs projections, and indices of translational and rotational diffusion. Results differed markedly from those for clusters of similar size obtained in simulations of argon and benzene systems and from experiments on charged clusters of SF6. All of the latter systems exhibited special stability at the magic number 13, but TeF6 clusters did not. The hexafluoride molecules rotated freely down to the lowest temperatures studied where the cluster's translations were all but frozen. A similar rotational freedom was not exhibited by benzene. When clusters were warmed they became progressively more fluxional, but the transition to liquid like behavior was more gradual than for the other systems. These differences in behavior of small clusters of the different systems are correlated with the preferred molecular packing arrangements and linked to the phase behavior of large clusters where the hexafluorides exhibit a much more diverse structural chemistry.