Temperature dependence of ozone rate coefficients and isotopologue fractionation in 16O–18O oxygen mixtures

The temperature dependence of five ozone isotope-specific rate coefficient ratios and of isotopologue fractionation has been determined. Large formation rate coefficient ratios of 1.5 like 16O+18O18O vs. 16O+16O16O show no temperature dependence while small ratios such as 18O+16O16O vs. 16O+16O16O with a value of 0.92 decrease with decreasing temperatures. Temperature-related changes of isotopologue fractionation values for 50O3 and 52O3 are explained in terms of changes in rate coefficient ratios and contributions from isotope exchange reactions. The latter reactions exclusively control the large isotope fractionation of 54O3 while the rate coefficient ratio 18O+18O18O vs. 16O+16O16O remains constant at 1.02.