Ion-molecule reactions of the rare gases with hydrogen. Part 1.—Diatomics-in-molecules potential energy surface for ArH +2

Abstract

Potential energy surfaces for the reactions Ar⁺+ H₂→ArH⁺+ H and Ar + H⁺₂→ArH⁺+ H (ArH⁺ in the ground state) are calculated by the method of diatomics-in-molecules (DIM), the theory of which is conveniently summarized in matrix notation. Diatomic ArH⁺ and ArH curves needed for the method are obtained from ab initio SCFMO calculations. The shape of the ArH⁺₂ surface appears to be consistent with the known experimental information for this system. Approximate calculations of collinear surfaces for the ground states of KrH⁺₂ and NeH⁺₂ are obtained by appropriate scaling of the ArH⁺ diatomic curves. Comparison of these surfaces with the ArH⁺₂ surface results in a consistent rationalization of the available experimental data on the rare gas-hydrogen ion-molecule reactions. Gross differences in the behaviour of these reactions are related primarily to changes in the ionization potentials of the rare gas atoms. This has a profound effect on the shapes of the potential energy surfaces, particularly in the entrance valley, where there is a crossing between surfaces associated with the differently charged reactant species.