Rate constant for the reaction of O(3P) with HBr from 221 to 455 K

Absolute rate constants for the reaction O(3P)+HBr→OH+Br have been measured over the temperature range 221–455 K using the flash photolysis technique combined with resonance fluorescence detection of O(3P) atoms. For each of the five temperatures at which the reaction was studied, the rate constant was shown to be independent of variations in [HBr], total pressure (Ar), and flash intensity (i.e., initial [O]). A linear least-squares treatment of the data in Arrhenius form yields the expression k7=(6.73±1.93)×10−12 exp(−1537±81/T) cm3 molecule−1 s−1 for 221≤T≤455 K, where the indicated errors are at the one standard deviation level. There is a suggestion of curvature in the Arrhenius plot below 298 K. These results are compared with two previous studies of the temperature dependence which covered a narrower range of temperatures and used O+NO chemiluminescence to monitor O(3P). Consistency with an estimate of k7 at 773 K is evaluated and rate constants for atomic bromine reactions derived from a study of the HBr inhibited thermal H2/O2 reaction at this temperature are examined in light of recent direct measurements. Comparison is also made of the activation energy measured here for the O+HBr reaction with recent calculations employing a modified bond energy–bond order method.