Photoionization of ozone: Formation of O4+ and O5+

Abstract

Ionization yields of O⁺, O₂⁺, and O₃⁺ have been studied as a function of wavelength in the photoionization of ozone from threshold to 600 Å with the primary process being the production of O₃⁺. The ratio O₃⁺ : O₂⁺ : O⁺ at 600 Å is 1.00 : 0.36 : 0.05. The adiabatic ionization potential of O₃⁺ is 990.32±0.3 Å (12.519±0.004 eV). Steplike structure occurs near threshold, at wavelengths corresponding to vertical ionization potentials reported in photoelectron spectroscopy studies. A weak onset for O₂⁺ production appears at 13.08₂ eV (947.7 Å), followed by more intense O₂⁺ production at 13.43₂ eV (932.2 Å). The onset for O⁺ formation appears weakly at 15.21 eV, rising continuously with decreasing wavelength. The formation of O₅⁺ via the ion–molecule reaction O₃⁺+O₃→O₅⁺+O was also observed and measured as a function of wavelength. The O₄⁺ ion was also detected. Pressure dependences and enthalpy considerations make the reaction O₃⁺+O₂→O₄⁺+O a highly probable mechanism for O₄⁺ formation.