Potential energy surface for the M₂X⁺ ion and the ionization potential of M₂X

Abstract

Potential energy surfaces for the M₂X⁺ ions (M denotes alkali atom, X halogen atom) have been calculated by a classical ionic model based upon the Rittner model. In all cases M₂X⁺ has substantial binding energy (∼1·5–2 eV) with respect of M⁺ + MX. The most stable configuration varies from linear for heavy M light X, to strongly bent for light M heavy X. The adiabatic ionization potential of the M₂X molecule I _ad (M₂X) is found to be surprisingly low; less than that of the alkali atom I(M). The vertical ionization potential I _v(M₂X) is only slightly greater than the adiabatic value. This facilitates a second electron jump in the reactions of alkali dimers with polyhalide and alkyl halide molecules. The main implications of the M₂X⁺ potential surface for the dynamics of the reaction M⁺ + M′X → MX + M′⁺ are briefly noted.