Potential energy surface for interactions between N₂ and He: Ab initio calculations, analytic fits, and second virial coefficients

An ab initio potential energy surface (PES) for the interaction of rigid N₂ with He is calculated by supermolecular fourth-order Møller-Plesset perturbation theory. The computations involve full counterpoise corrections and large basis sets including bond functions. The 61 ab initio points on the PES are fitted to a 21-parameter algebraic form with an average absolute error of 0.39% and a maximum error less than 1.2%. The characteristics of the fitted PES are compared with those of previous surfaces. Unlike the older surfaces, our PES has the anisotropy thought to be required for a proper description of experimental data. Pressure second virial coefficients are calculated from our surface and compared with experimental values.