Production of isotopically heavy ozone by ultraviolet light photolysis of O2

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