State-selected charge-transfer and rearrangement reactions in four-atom ion–molecule systems

Abstract

An extensive study of charge transfer and chemical (rearrangement) reactions in four-atom ion–molecule systems (AB + CD)⁺, where each of AB and CD stands for a diatomic molecule, has been performed by selecting vibrational and vibronic states of reactant ions using the ‘TESICO’ coincidence technique. Systems studied include (H₂+ N₂)⁺, (HD + N₂)⁺, (D₂+ N₂)⁺, (O₂+ H₂)⁺, (NO + H₂)⁺ and (N₂+ O₂)⁺, and the reactions starting from both AB⁺+ CD and AB + CD⁺ have been studied in each system. Some systems show exactly the same vibrational state dependence for the charge transfer and chemical reactions, while some others show quite different dependence between the two channels. It has also been found that the two reactions AB⁺+ CD and AB + CD⁺ leading to the same product ABC⁺ show sometimes similar and sometimes dissimilar internal energy dependences. The experimental internal-state dependence is compared with that calculated from a model appropriate to a long-range electron-jump mechanism. Based on this comparison, some features of the potential-energy surfaces for each system are discussed.