Rate coefficient for the reaction of CCl 3 radicals with ozone

The rate coefficient for the reaction of CCl 3 radicals with ozone has been measured at 303 ± 2 K. The CCl 3 radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl 3 concentration was monitored with a photoionization mass spectrometer. Addition of the O 3 –O 2 mixture to this system caused a decay of the CCl 3 concentration because of the reactions of CCl 3 + O 3 → products (5) and CCl 3 + O 2 → products (4). The decay of signals from the CCl 3 radical was measured in the presence and absence of ozone. In the absence of ozone, the O 3 –O 2 mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl 3 + O 2 could be determined separately, the absolute rate coefficient for reaction (5) was obtained from the competition among these reactions. The rate coefficient determined for reaction (5) was (8.6 ± 0.5) × 10 −13 cm 3 molecule −1 s −1 and was also found to be independent of the total pressure (253–880 Pa of N 2 ). This result shows that the reaction of CCl 3 with O 3 cannot compete with its reaction with O 2 in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003