Kinetics of ozone formation in the pulse radiolysis of oxygen gas

Abstract

The kinetics of O₃ formation after an electron pulse have been studied in O₂, at pressures from 7 to 400 kN m^–2, by optical absorption measurements in the range 250–330 nm. The absorption spectra at different times and the time-dependence of the absorption at 250, 270 and 310 nm are interpreted in terms of three, kinetically distinguishable, consecutive reactions: O + O₂+ O₂ [graphic omitted] O^α₃+ O₂, ^α₃+ O₂ [graphic omitted] O^β₃+ O₂, O^β₃+ O₂ [graphic omitted] O₃+ O₂. The intermediates, O^α₃ and O^β₃, which are assumed to be vibrationally excited O₃, have broad absorption with maxima at approximately 310 and 285 nm respectively. The kinetic analysis leads to a value of k₁= 5.4 ± 0.3 × 10^–34 cm⁶ molecule^–2 s^–1 and also gives values for the rate constants of the reactions which deactivate excited O₃.

In mixtures of O₂ with various other gases, values have been obtained for the rate constants of the reactions O + O₂+ M[graphic omitted]O^α₃+ M, k_1a= 2.7 ± 0.3, 13.0 ± 1.5, 13.3 ± 1.2, 31 ± 3 × 10^–34 cm⁶ molecule^–2 s^–1 for M = Ar, N₂O, CO₂, SF₆ respectively. CO₂ and SF₆ are efficient deactivators of excited O₃; values are reported for the rate constants for deactivation of O^β₃ by these molecules.