On the adequacy of pairwise additive potentials for rare gas–halogen systems: The effect of anisotropy of interactions between atoms

Abstract

A simple model is presented for the potential energy functions of rare gas dihalides RgX2, which uses empirical potentials for diatomic fragments and takes properly into account anisotropic interactions between atoms, resulting in diabatic potentials which correlate with the ground state X2 molecule and Rg atom. Specific results are obtained for potential energy surfaces of ArX2 (X =F, Cl, Br, I) complexes and compared to those from several widely used models based on pairwise additive isotropic interactions. All these earlier models are found to underestimate the binding in the linear geometry, predicting a complete absence of a linear bound state; this feature is especially significant for ArF2 in which the anisotropic model predicts the linear configuration to be more stable. The new anisotropic model leads to Ar–X2 dissociation energies in good agreement with experiments.