SPECTROSCOPY AND DYNAMICS OF RARE GAS-SPHERICAL TOP COMPLEXES - THE INFRARED-SPECTRUM OF THE NU(3) BAND OF ARGON-SILANE

The infrared spectrum of Ar-SiH4; a rare gas-spherical top van der Waals complex, has been recorded in the vicinity of the silane nu(3) triply degenerate stretching vibration similar to 2189 cm(-1). A complex, dense spectrum is observed, and this is due to the observation of 12 bands with origins corresponding to transitions between different internal rotor states of the silane molecule within the complex. From the analysis of the rotational structure within each band, the average argon-silane separation is determined to be 4.043 Angstrom in the ground vibrational state and 4.046 Angstrom, in the excited vibrational state with nu(3) = 1 Using a model developed previously and a very simple form for the intermolecular potential, these 12 bands have been assigned and an effective anisotropic intermolecular potential for the internal rotation of the silane molecule within the complex has been determined. The vibrational anisotropy responsible for lifting the threefold degeneracy of the nu(3) vibration is found to be fairly small, of the order of 1 cm(-1), while the rotational anisotropy is much larger, of the order of 90 cm(-1).