Collision-induced rototranslational spectra of H2-Ar from an accurate ab initio dipole-moment surface.

Abstract

The induced dipole moment of hydrogen- (${\mathrm{H}}_{2}$) argon pairs is obtained with an estimated accuracy of about 2% by treating the collisional complex like a molecule in self-consistent-field (SCF) and coupled-electron-pair calculations. The basis-set superposition error is effectively avoided by the use of nonorthogonal local orbital sets. Based on the four-term, ab initio, orientation-dependent dipole function and a reliable isotropic potential model, the rototranslational absorption spectra of free and bound ${\mathrm{H}}_{2}$-Ar pairs are computed from an exact quantum formalism. Both the spectral profile and absolute intensity of the ab initio spectra are shown to be in agreement with Dore and Birnbaum's recent measurement. The work demonstrates once more what was seen previously for the He-Ar and ${\mathrm{H}}_{2}$-He far-infrared absorption spectra, namely that the precision attainable in such ab initio computations matches or exceeds that of the best available measurements of the same spectra [Meyer and Frommhold, Phys. Rev. A 33, 3807 (1986), and Phys. Rev. A 34, 2771 (1986).