Anisotropic intermolecular forces

Abstract

Anisotropic potential energy surfaces for Ne·HCl, Kr·HCl and Xe·HCl are obtained by simultaneous least squares fitting to molecular beam spectra and rotational line broadening cross sections. A revised potential surface for Ar·HCl is also presented. The potentials are all very similar in shape, with the absolute minimum at the linear rare gas—HCl geometry in each case. The absolute well depths and well depth anisotropies increase steadily as the size of the rare gas atom increases.

The potentials should be reliable in the region of the absolute minimum and on the repulsive wall of the potential. The molecular beam spectra for Ne·HCl can be fitted only by a potential with a significant secondary minimum at the linear Ne·Cl-H geometry, but the existing data for the more anisotropic Ar, Kr and Xe systems are not sensitive to the presence of this potential feature. The potential surfaces for these systems have accordingly been constrained to have a similar secondary minimum near the linear rare gas-ClH geometry. Experiments which would provide further information on the intermolecular potentials are suggested and predictions of the results are made.