Kinetics of the gas phase reaction of hydroxyl radicals with ethane, benzene, and a series of halogenated benzenes over the temperature range 234–438 K

Absolute rate constants for the gas phase reactions of OH radicals with ethane ( k 1 ), benzene ( k 2 ), fluorobenzene ( k 3 ), chlorobenzene ( k 4 ), bromobenzene ( k 5 ), iodobenzene ( k 6 ), and hexafluorobenzene ( k 7 ) have been measured over the temperature range 234–438 K using the flash photolysis resonance fluorescence technique. The rate constants measured at room temperature (296 K), at total pressures of argon diluent between 25 and 50 Torr, were (in units of 10 −13 cm 3 molecule −1 s −1 ): k 1 = (2.30 ± 0.26), k 2 = (12.9 ± 1.4), k 3 = (6.31 ± 0.81), k 4 = (7.41 ± 0.94), k 5 = (9.15 ± 0.97), k 6 = (13.2 ± 1.6), and k 7 = (1.61 ± 0.24), respectively. The indicated errors are our estimate of 95% confidence limits and include two standard deviations from the least‐squares analysis together with an allowance for any possible systematic errors in the measurements. At elevated temperatures and under pseudo‐first‐order reaction conditions, non‐exponential hydroxyl radical decays were observed for benzene and the monosubstituted halo‐aromatics. For ethane and hexafluorobenzene, exponential decays were observed over the complete temperature range and the data were fit by the Arrhenius expressions: k 1 = (8.4 ± 3.1) × 10 −12 exp[(−1050 ± 100)/ T ] and k 7 = (1.3 ± 0.3) × 10 −12 exp[(−610 ± 80)/ T ], respectively. The results are compared with previous literature data and the mechanistic implications are discussed.