Ab initio potential energy surfaces of the ion-molecule reaction: C ₂H ₂+O ⁺

The mechanism of early stage of the chemical reaction was investigated by performing high level ab initio calculations on potential energy surfaces (PES) for several low lying excited states for O ⁺ + C ₂H ₂ collision system. The key pathways to form charge-transfer (CT) products and the covalently bound intermediates were also investigated. The transition state TS1 was found to be caused by the avoided crossing between the reactant and CT2 electronic states. The results show that charge transfer and chemical reaction products are detected above 35 and 39 kcal/mol collision energies, respectively.