Calculations of structures and vibrational spectra of homogeneous and mixed SF6 clusters with Ar

A recently reported intermolecular potential for SF₆, featuring exchange, dispersion, and electrostatic terms, is used to determine minimum energy structures of homogeneous SF₆ clusters up to the decamer. By adding appropriate interaction terms, also structures of mixed (SF₆)₂-Ar_n clusters are calculated. A second order line shift formalism, treating the anharmonic intramolecular force field and the intermolecular potential as a perturbation, is employed to calculate the corresponding IR-spectra in the region of the n₃nu _{3} vibrational mode of the monomer (at 947.968 cm^-1). The leading interaction mechanism responsible for the line shifts is confirmed to be the resonant dipole-dipole coupling. The theoretical spectra fairly describe both size-selected spectra for clusters up to the tetramer and recently measured FT-IR spectra in a continuous supersonic Laval nozzle flow.