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
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