TEMPERATURE-DEPENDENT RATE CONSTANTS AND PRODUCT BRANCHING RATIOS FORTHE GAS-PHASE REACTION BETWEEN CH3O2 AND CLO

Kinetic and product branching data have been measured for the reaction of CH3O2 radicals with CIO in the temperature range 225-355 K using t he discharge-flow/mass spectrometry technique. The pressure-independen t overall reaction rate constant is described by k(12)(225-355 K) = (3 .25 +/- 0.50) x 10(-12) exp((-l 14 +/- 38)/ T) cm3 molecule-1 s-1. Two reaction channels were identified, leading to CH3O + ClOO (12a) and C H3OCl + O2 (12b), respectively. The branching ratios, alpha12a = k12a/ k12 and alpha12b = k12b/k12, are also independent of pressure and are described by alpha12a = (1.51 +/- 0.56) exp((-218 +/- 93)/T) and alpha 12b = (0.080 +/- 0.059) exp((377 +/- 178)/T). These expressions yield roughly equal rate constants of k12a and k12b of ca. 1 X 10(-12) cm3 m olecule-I s-1 at the low temperatures prevalent in the polar winter an d early springtime stratosphere. We thus identify CH3OCl as a potentia lly important species in ozone hole chemistry.