Ion momentum imaging study of the ion–molecule reaction Ar+ + O2 → Ar + O2+
Charge exchange reactions between Ar+(2P) and O2 (X3Σ−g) 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 O2+ is enhanced gradually with the increase of collision energy, and the forward-scattered O2+ 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 O2+ at the a4Πu state. At the higher collision energies, besides a4Πu and the high-lying states that are visible in the photoionization process, the O2+ 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+.