Molecular Orbital Correlations and Ion–Molecule Reaction Dynamics

Abstract

We examine the application of molecular orbital correlation diagrams to ion–molecule collision processes. In situations where the reactant and product orbitals are few in number and well spaced in energy, the correlation diagrams give a clear picture of how the reactant electron configuration evolves to that of the products. The diagrams lead to a simple explanation of why the endothermic H₂⁺(He, H)HeH⁺ and H₂⁺(Ne, H)HeH⁺ reactions occur, whereas the exothermic processes He⁺(H₂, H)HeH⁺ and Ne⁺(H₂, H)NeH⁺ have undetectably small cross sections. Similarly, it is possible to use the diagrams to explain why the CO⁺(H₂, H)HCO⁺ and N₂⁺(H₂, H)N₂H⁺ reactions proceed by direct interaction mechanisms despite the substantial stability of the intermediate ions H₂CO⁺ and N₂H₂⁺. Several other applications of the diagrams are discussed.