Photoionization study of the reaction O+2 (a 4Πu) with O2†

Abstract

A high−resolution photoionization study of the production of O⁺₃ from the reaction of O⁺₂ (a ⁴Π_u) with O₂ determined that the reaction proceeds primarily through the v′ = 5 to 10 vibrational levels of the O⁺₂ (a ⁴Π_u) state. The relative reaction cross section for O⁺₃ formation increases rapidly from v′ = 4 to v′ = 9 where it is a maximum. For v′ = 10, the lowest vibrational level for which the reaction O⁺₂ (a ⁴Π_u) + O₂ → O⁺₂ + O + O is exothermic, the reaction cross section for observable O₃⁺ is approximately 10% smaller than the cross section for v′ = 9, and for v′ ? 11 the cross section is relatively small. A study of the cross section as a function of translational energy showed that internal vibrational energy is significantly more effective than translational energy or product formation for total collision energies of up to ∼1 eV above threshold. A plausible surface crossing mechanism for the reaction is suggested. The calculated thermodynamic threshold for O⁺₃ production corresponds to a wavelength of 747.2±1.4 Å, which nearly coincides with O⁺₂ (a ⁴Π_u, v′ = 4) convergence limit at 747.25 Å. A very small amount of reaction is observed at this vibrational convergence limit, however this is due at least in part to the thermal rotational and translational energy of the reactants.