Intermolecular Potentials from Crossed Beam Differential Elastic Scattering Measurements. V. The Attractive Well of He2

Abstract

The van der Waals well of the helium pair potential has been studied by crossed molecular beam elastic scattering measurements. Low energy helium beams were produced by specially designed beam sources cooled with liquid hydrogen. Only five partial waves were found to contribute significantly to the differential cross section. A multiparameter potential function is used to construct the interatomic potential from experimental results. The potential parameters describing the location and depth of the attractive well are given by ${\text{ε=11.0± 0.2}}^{\mathrm{o}}\mathrm{K}{\mathrm{,\hspace{0.17em}r}}_m\text{=2.963± 0.01}$ Å . The potential does not contain a bound state of zero angular momentum. Comparisons with other He₂ potentials based on bulk properties and ab initio calculations are presented; the temperature dependence of the second virial coefficient is also discussed for the proposed potential.