Ionic reactions occurring in the irradiation of carbon dioxide – oxygen mixtures at very high dose rates

Abstract

Ozone yields have been measured in CO2–O2 mixtures irradiated with single pulses from a Febetron 705 at a dose rate of 1026 eV g−1 s−1. Low concentrations of carbon dioxide in oxygen rapidly reduce the yield from G(O3) = 12.8 to G(O3) ≈ 9. At 300 Torr total pressure, as the oxygen concentration is reduced, the ozone yield decreases from this yield of G(O3) ≈ 9 to an extrapolated yield, at zero oxygen, of close to G(O3) = 7.8. Changes of yields with composition are explained in terms of ionic reactions, the main neutralization process being[Formula: see text]At 700–1500 Torr total pressure, the ozone yields are lower than that at 300 Torr. It is proposed that clustering of the ionic species affects the products of the neutralization reaction.Sulfur hexafluoride suppresses the dissociative neutralization reaction and ozone yields from mixtures containing 1.5–2% SF6 are those predicted from direct neutral dissociation processes in the pure gases.Computer calculations are used to compare the experimental results to the proposed mechanism and, in general, a good fit is obtained.