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 Waa ls complex, has been recorded in the vicinity of the silane nu(3) trip ly degenerate stretching vibration similar to 2189 cm(-1). A complex, dense spectrum is observed, and this is due to the observation of 12 b ands with origins corresponding to transitions between different inter nal rotor states of the silane molecule within the complex. From the a nalysis of the rotational structure within each band, the average argo n-silane separation is determined to be 4.043 Angstrom in the ground v ibrational state and 4.046 Angstrom, in the excited vibrational state with nu(3) = 1 Using a model developed previously and a very simple fo rm for the intermolecular potential, these 12 bands have been assigned and an effective anisotropic intermolecular potential for the interna l rotation of the silane molecule within the complex has been determin ed. The vibrational anisotropy responsible for lifting the threefold d egeneracy of the nu(3) vibration is found to be fairly small, of the o rder of 1 cm(-1), while the rotational anisotropy is much larger, of t he order of 90 cm(-1).