HOMOGENEOUS AND MIXED UF6 CLUSTERS WITH AR - CALCULATIONS OF STRUCTURES AND VIBRATIONAL-SPECTRA

A recently developed site-site intermolecular potential for UF6, featu ring exchange, dispersion, and electrostatic terms, is used to calcula te minimum energy structures of homogeneous UF6 clusters up to the dec amer. The structures of mixed (UF6)(2)-Ar-n clusters are also calculat ed by adding appropriate interaction terms. The IR spectra correspondi ng to the determined cluster structures in the region of the nu(3) vib rational mode of the monomer (at 627.724 cm(-1)) are calculated using a second-order line shift formalism, treating the anharmonic intramole cular force field and the intermolecular potential as a perturbation. The leading interaction mechanism responsible for the line shifts of t he nu(3) mode is found to be the electrostatic one (implicitly the res onant dipole-dipole coupling). The theoretical spectra are shown to sa tisfactorily describe the peaks around 623, 632, and 640 cm(-1) found in the recently measured Fourier transform IR spectra in a continuous supersonic Laval nozzle flow and attributed to the clusters formed by UF6. (C) 1998 American Institute of Physics. [S0021-9606(98)00933-X].