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.

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