Third-body dependence of rate coefficients for ozone formation in 16O–18O mixtures

Two ozone rate coefficient ratios have been measured in different bath gases that include noble gases, O2/N2 mixtures as well as CH4 and CO2. While absolute rate coefficients for ozone formation differ by a factor of four between Ar and CO2 the rate coefficient ratios for 16O+18O18O/16O+16O16O and 18O+16O16O/18O+18O18O remain the same in all bath gases, the first ratio being over 50% higher than the second. This suggests that the ozone isotope effect maybe discussed within the framework of the Lindemann–Hinshelwood mechanism but with isotope specific steps: The selectivity arises in the first collision between O+O2 which produces the activated complex O3* and does not come from the subsequent collisional deactivation and stabilisation through the third body.