Third-body dependence of rate coefficients for ozone formation in [formula omitted] mixtures

Abstract

Two ozone rate coefficient ratios have been measured in different bath gases that include noble gases, O 2/N 2 mixtures as well as CH 4 and CO 2. While absolute rate coefficients for ozone formation differ by a factor of four between Ar and CO 2 the rate coefficient ratios for 16 O+ 18 O 18 O/ 16 O+ 16 O 16 O and 18 O+ 16 O 16 O/ 18 O+ 18 O 18 O 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+O 2 which produces the activated complex O 3 * and does not come from the subsequent collisional deactivation and stabilisation through the third body.