An ab initio coupled Hartree-Fock calculation of the nuclear shielding in the H₂/He interacting system

Abstract

A coupled Hartree-Fock scheme has been used to calculate the elements of the nuclear shielding tensors in the H₂/He interacting system. The effects of the basis set size and the choice of origin for the magnetic vector potential have been examined. The results of the calculation lead to several estimates of the repulsive contribution to the N.M.R. shielding virial coefficient σ _{h 2 he}, the best one of which is + 3 ppm cm³ mol^-1. Although an experimental value of the virial coefficient is unavailable for the H₂/He system, results for other mixtures have the same order of magnitude but an opposite sign. This suggests in general that, though attractive contributions are predominant in affecting the shielding changes due to intermolecular interaction, the repulsive contributions are by no means negligible as has sometimes been assumed.