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 O-16 + (OO)-O-18-O-18 vs. O-16 + (OO)-O-16-O-16 show no temperature dependence while small ratios such as O-18 + (OO)-O-16-O-16 vs. O-16 + (OO)-O-16-O-16 with a value of 0.92 decrease with decreasing temperatures. Temperature-related changes of isotopologue fractionation values for O-50(3) and O-52(3) 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 O-54(3) while the rate coefficient ratio O-18 + (OO)-O-18-O-18 vs. O-16 + (OO)-O-16-O-16 remains constant at 1.02. (C) 2002 Elsevier Science B.V. All rights reserved.