Kinetics of the reactions of the hydroxyl radical with molecular chlorine and bromine

Abstract
The rates of the reactions of OH with Cl2 and Br2: OH + Cl2→ HOCl + Cl, ΔH 298= 4.3 kJ mol–1(1), OH + Br2→ HOBr + Br, ΔH 298=–38.05 kJ mol–1(2) have been investigated over a range of temperatures between 253 and 333 K by using a discharge-flow resonance-fluorescence technique. At 293 K the rate constants for reactions (1) and (2) are k1=(6.8 ± 1.0)× 10–14 cm3 molecule–1 s–1, k2=(3.4 ± 1.2)× 10–11 cm3 molecule–1 s–1. The rate constant for the reaction of OH with Cl2 increases with temperature, and can be fitted between 253 and 333 K by the following Arrhenius expression: k1=(1.7+4.4 –1.2)× 10–12 exp –(911 ± 373)/T cm3 molecule–1 s–1. For the reaction of OH with Br2, the data are consistent with a zero activation energy, although a small activation energy (not exceeding 5 kJ mol–1) could also be supported.

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