Ab initio study of the O2(X 3Σg−)+Ar(1S) van der Waals interaction

Abstract

A potential energy surface for the Ar(1S)+O2(X 3Σg−) interaction is calculated using the supermolecular unrestricted Mo/ller–Plesset (UMP) perturbation theory and analyzed via the perturbation theory of intermolecular forces. The global minimum occurs for the T-shaped geometry, around 6.7 a0. Our UMP4 estimate of the well depth of the global minimum is De=117 cm−1 and the related ground state dissociation energy obtained by diffusion Monte Carlo calculations is 88 cm−1. These values are expected to be accurate to within a few percent. The potential energy surface also reveals a local minimum for the collinear geometry at ca∼7.6 a0. The well depth for the secondary minimum at the UMP4 level is estimated at De=104 cm−1. The minima are separated by a barrier of 23 cm−1. The global minimum is determined by the minimum in the exchange repulsion in the direction perpendicular to the O–O bond. The secondary, linear minimum is enhanced by a slight flattening of the electron density near the ends of the interoxygen axis.