Knowledge Bank

The best existing potential energy surfaces for the $H2$-rare gas systems were determined from an analysis based largely on the discrete infrared spectra associated with the $v=1-0$ fundamentals of the $H2$ or $D2$ components of these complexes.1 However, McKellar has now observed transitions of $H2$-Ar involving excited van der Waals stretching states, as well as spectra associated with the component diatom undergoing pure rotational $(S0(0),S0(1))$ and first overtone vibrational $(Q2(1),S2(0)$ and $S2(1))$ $transitions.2$ The present paper describes our use of these new data, in conjunction with microwave spectra, and elastic and inelastic differential cross section measurements, to determine an improved potential energy surface for the $H2$-Ar system. The present analysis is the first to take account of the excited stretching states of the van der Waals bond; hence it should yield an improved characterization of the shape of the potential along the atom-diatom separation coordinate. In addition, the inclusion of data involving the hydrogen overtone transitions should lead to a better representation of the diatom-stretching-dependence of the potential energy surface, while the far infrared data should better characterize the stretching-dependence of the potential anisotropy. The current status of this analysis, as well as the applicability of of the methods developed to other more strongly-anisotropic systems, will be discussed.