New experimental evidence for the mechanism for production of isotopically heavy O3

Abstract

The mass independent isotopic fractionation in O3 formation from O2 photolysis has been investigated as a function of pressure (2.1‐760 Torr), UV wavelength and differing third body. In the low pressure regime (⪝ 200 Torr room temp., ⪝ 10 Torr liquid nitrogen), O3 decomposition occurs, resulting in a secondary, mass‐dependent isotopic fractionation. It is demonstrated that wall effects produce O3 in a mass‐dependent fashion, thus indicating the involvement of rotational states in the mass independent fractionation process. For pressures in the intermediate range, to ∼600 Torr, a single‐stage fractionation is observed, presumably with δ17O≅δ18O≅85‐100‰, though secondary effects may be operative also. At pressures above 450 Torr, the δ18O of O3 decreases to 87‰ at 760 Torr. The fractionation process appears to be independent of UV wavelength and third body composition; photolysis of air produces O3 isotopically similar to pure O2 photolysis at comparable pressures.