Non-Dissociative Single-Electron Capture Studied for O2^2+ Ions on Ar, N2 and He at 100 eV

Energy-gain spectra for single-electron capture by O2^2+ ions colliding with Ar, He and N2 have been measured at an impact energy of 100 eV and 0° scattering angle by means of translational energy-gain spectroscopy. In O2^2+ - Ar and N2 collisions, only one peak is observed at the energy-gain around 3.5 eV, which is correlated with nondissociative single-electron capture from ground state (X^1 Σg^+) of O2^2+ ions into the A^2 Πu state of O2^+. However, for the O2^2+ - He collision system, the dominant channels are due to capture into the ground state X^2 Πg of O2^+ from W^3 Δu, B^3 Πg and B/^3 Σu^- metastable states of the O2^2+, respectively. A reasonable description of the dominant final states is obtained qualitatively in terms of the reaction windows, which are calculated using the Landau- Zener (LZ) model and the extended version of the classical over-the-barrier (ECOB) model. Differential cross sections for single-electron capture by 100 eV O2^2+ ions from Ar have also been measured. The results are quantitatively explained by semi-classical model based on Coulomb potential energy curves.