Collision-Energy Dependence of the Ion-Molecule Charge-Exchange Reaction Ar⁺ + CO → Ar + CO

Ion-molecule charge-exchange reactions Ar⁺ + CO → Ar + CO⁺ at the center-of-mass collision energies of 4.40, 6.40, and 8.39 eV are investigated using ion velocity map imaging technique. Although multiple electronically excited states of CO⁺ are accessed, the population of CO⁺ at the A²Π state is predominant in the present collision-energy range. In contrast to our previous study for NO, but similar to the case of O₂, the forward-scattered CO⁺ yields show a broader angular distribution at the higher collision energy. Typically, the Franck-Condon-region charge transfer, energy resonant charge transfer, and intimate collision are three different mechanisms in which the intimate collision experiences an intermediate complex, and this mechanism usually plays an essential role in the thermal-energy reactions. However, the present observations indicate that this mechanism, concerning the intermediate (Ar-CO)⁺, is still of utmost importance in a relatively high collision-energy range.