Production of isotopically heavy ozone by ultraviolet light photolysis of O2

Abstract

Ozone was produced by UV photolysis (157‐200nm) of molecular oxygen. The product ozone is enriched in 17O, 18O on a mass‐independent basis, similar to the fractionations observed in an electrical discharge. The magnitude of 18O, 17O enrichment decreases with decreasing pressure, suggesting the presence of two fractionation mechanisms with differing δ17O/δ18O ratios. One of the end members would be mass‐independent with δ18O ≅ δ17O ≅ 90‰, which is dominant above ∼ 20 torr. The second process which is significant below ∼ 6 torr produces O3 with δ18O ≅ − 55‰, δ17O ≅ − 27.5, possibly due to isotopic selectivity in diffusion to the reaction systems wall. The δ17O = δ18O isotopic fractionation resembles that observed in stratospheric ozone, though the magnitude of fractionation is a factor of four less. Copyright 1987 by the American Geophysical Union.