Bound atom–diatomic molecule complexes. Anisotropic intermolecular potentials for the hydrogen–rare gas systems

Abstract

Spectra of the van der Waals complexes H2–Ar, Kr, Xe, and D2–Ne have been analyzed to obtain anisotropic intermolecular potentials and transition dipole moments. The Morse-spline–van der Waals functional form is used to describe the potentials. Eigenvalues were computed by solving the close coupling equations, and calculated transition frequencies were fit to the experimental Q1(0) and S1(0) peak frequencies by a least squares technique. For this purpose experimental peaks were chosen from the P and R as well as the N and T branches of the spectra. The absorption was computed for each transition. The total absorption contour for a spectrum was obtained by assuming a Lorentzian line shape for the individual transitions and summing contributions from overlapping lines. The agreement between calculated and experimental absorption contours was excellent. For the Ar, Kr, and Xe complexes it was necessary to include three terms in the angular expansion of the transition dipole moment rather than the usual two terms. These three terms interfere to produce the complex absorption contours observed in some spectra. The anisotropy of the intermolecular potential was not determined completely. Rather, a linear relationship between the repulsive and attractive anisotropy coefficients is found.