Ab initio study of the H2CO–Ar complex

Abstract

The potential energy surface of the H2CO–Ar complex is calculated at the second-order Mo/ller–Plesset perturbation theory and analyzed using the perturbation theory of intermolecular forces. The equilibrium geometry (De=171 cm−1) involves a T-shape structure with the Ar atom nearly perpendicular to the C–O bond of H2CO and in the molecular plane of H2CO. The equilibrium configuration results from a minimum in the exchange repulsion. It is conceivable that H2CO undegoes a hindered internal rotation in the complex. A barrier to such a motion is estimated at 32 cm−1. The potential energy surface is very complex. The anisotropy of the surface involving the in-plane motion of Ar is very high and resembles that of the Ar–H2O complex. The anisotropy involving motion of Ar perpendicular to the molecular plane of H2CO is much weaker, and it is strikingly similar to that of the Ar–CO complex.