Ion momentum imaging study of the ion-molecule reaction Ar + O→ Ar + O.

Charge exchange reactions between Ar(P) and O (XΣ) are investigated in the collision energy range of 3.40-9.24 eV within the center-of-mass coordinate, by using the ion momentum imaging technique. The internal energy of the product O is enhanced gradually with the increase of collision energy, and the forward-scattered O ions are distributed in the broader range of scattering angle at higher collision energies. At the low collision energy of 3.40 eV, the resonant charge transfer, similar to a photon ionization process, leads to the Franck-Condon-like vibrational state population of O at the aΠ state. At the higher collision energies, besides aΠ and the high-lying states that are visible in the photoionization process, the O products could be populated at some electronically bound states in the non-Franck-Condon region. The present observations indicate again the strong collision-energy dependences of the charge exchange reactions, but distinctly different from our previous findings for Ar + NO → Ar + NO.