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.