Semiempirical Potential and Bound State of the Helium−4 Diatom

Hybrid potentials for the 4He–4He system composed of the theoretical short-range repulsion, an empirical potential at the minimum, and the theoretical long-range attraction have been constructed. Second virial coefficients calculated for these potentials are in poor agreement with experimental data. A semiempirical potential is constructed which fits the data well. This potential becomes the theoretical interaction at large separations; its gross features are a core radius of 2.645 Å and a potential minimum of −1.73×10−15 erg at 2.975 Å. There is one weakly bound state of the helium−4 diatom with a binding energy of roughly 0.01°K. An analysis of the effect of uncertainties in the experimental data upon these results is included; the bound state remains even with the allowed uncertainties.