Molecular dynamics simulation of the homogeneous nucleation of UF6 molecules: Configurations and infrared spectra of the excited hot clusters

The temperature, potential energy, and configurations of the clusters produ ced in the homogeneous nucleation of UF6 molecules from the supercooled (su persaturated) vapor phase were determined by classical molecular dynamics ( MD) simulations. We observed two phenomena which demonstrate that the nucle ation process occurs in the state far from thermal equilibrium. First, the excited hot clusters, the temperature of which is much higher than that of the monomer, were produced and continued to exist during the nucleation pro cess. Second, the relationship between the potential energy and temperature of the clusters depends on the monomer temperature, that is, the potential energy at a temperature decreases with the increase in monomer temperature . In the simulations, various types of cluster configurations were observed : prolate, oblate, spherelike, and confeitolike. The confeitolike cluster i s composed of one core and a few horns, and it was found predominantly in t he hotter clusters. The infrared spectra of the UF6 clusters were calculate d using a dipole-dipole and dipole-induced dipole interaction model and com pared with those measured in a supercooled state by Tanimura [J. Chem. Phys . 107, 7096 (1997)]. As a result, we found that the spectra measured in the supercooled state can be attributed to the excited hot clusters, the confi guration of which are confeitolike. (C) 2000 American Institute of Physics. [S0021-9606(00)50308-0].