Rate constants for the reactions of metastable O+ ions with N2 and O2 at collision energies 0.04 to 0.2 eV and the mobilities of these ions at 300 K

Abstract

The reactions of metastable O⁺* ions with N₂ and O₂ have been examined in a selected‐ion flow‐drift tube over the relative kinetic energy range from thermal to 0.2 eV. The rate constants are found to be (8.5±3.4)×10⁻¹⁰ and (8.1±3.2)×10⁻¹⁰ cm³ s⁻¹, respectively, at these energies. These values are essentially equal to the gas‐kinetic limiting values. The principal reaction mechanism in both cases is charge transfer. Based on molecular beam studies of the ion‐source reaction thought to produce the present O⁺* ions, it appears likely that they are largely O⁺(²D°) ions. The present results for these reactions are in good agreement with the results of most of the earlier studies, which were limited to either thermal or elevated collision energies. However, the present data for O⁺*+N₂ appear to conflict with the much smaller rate constant predicted for the reaction of O⁺(²D°)+N₂ from analyses of satellite data. As a necessary part of this study, the mobilities of the O⁺* ions in helium were determined and are 7% to 11% less than those of the ground‐state O⁺ ion.