Intermolecular potentials and isotope effects for molecular hydrogen–inert gas complexes

Abstract

An exact power series expansion is derived which interrelates the coefficients of the Legendre expansions for an atom–diatomic molecule potential function expanded about the centers of mass of two different isotopes of the diatomic. Its application to the anisotropic potential recently obtained for H₂– and D₂–Ar yields a potential for HD–Ar, which is then used to predict the transition frequencies in the infrared absorption spectrum of the latter. The relatively large discrepancies between these predictions and the recent measurements of McKellar [J. Chem. Phys. 61, 4636 (1974)] are attributed to the unusual sensitivity of such predictions to the shape of the isotropic potential in the region between its minimum at R_e⁽⁰⁾ and its zero energy turning point, σ⁽⁰⁾.