Measurements of the O+ + N2 and O+ + O2 reaction rates from 300°K to 2 eV

Abstract

The rates and energy dependences of the reactions ${\mathrm{O}}^{+}+{\mathrm{N}}_2\to {\mathrm{NO}}^{+}+\mathrm{N}$ and ${\mathrm{O}}^{+}+{\mathrm{O}}_2\to \mathrm{O}+{\mathrm{O}}_2^{+}$ have been studied in a drift tube/mass spectrometer apparatus. At 300°K rate coefficients of (1.2 ± 0.2) × 10⁻¹² and (2.0 ± 0.2) × 10⁻¹¹ cm³/sec are found for the reactions with N₂ and O₂, respectively. The rate coefficients at 300°K and their variation with ion energy are in satisfactory agreement with previous results of flowing afterglow studies carried out at temperatures up to 600°K. At ion energies above ∼ 0.15 eV for O⁺ + N₂ and ∼ 0.25 eV for O⁺ + O₂ the rates are observed to increase sharply, a behavior anticipated on the basis of extrapolations to low energies of ion beam results. Both reactions are of particular importance in converting atomic O⁺ ions in the Earth's ionosphere (E and F regions) into molecular ions. The present measurements extend previous rate coefficient determinations to ion energies appropriate to F region conditions (500°K < T < 2000°K).