Collision-Energy Dependence of the Ion-Molecule Charge Exchange Reaction Ar + NO.

High-lying quantum states of molecule are apt to be populated by translational-to-internal energy transfer in the collisions with atom, which usually becomes more significant with the increase of collision energy. However, in the charge exchange reaction Ar + NO → Ar + NO, the products NO prefer a dominant population at the lowest triplet state aΣ, in particular, in the higher energy collisions; the higher states bΠ and wΔ of NO are accessed only at the lower collision energies. Such a striking collision-energy dependence is attributed to two distinctly different processes: the former is controlled with an energetically resonant charge-transfer mechanism; while the latter experiences an intermediate complex (Ar-NO) which permits a more efficient translational-to-internal energy transfer.