Kinetics of the reactions of OH with several alkyl halides

Abstract

The rate coefficients for the reactions of OH with methyl chloride (k₁), ethyl chloride (k₂), methylene chloride (k₃), ethyl bromide (k₄), n-propyl bromide (k₅) and isopropyl bromide (k₆) were measured over the temperature range, 220–380 K, using pulsed photolysis-pulsed laser induced fluorescence (PP-PLIF). The measured rate coefficients, k_1–6 , (cm³ molecule⁻¹ s⁻¹) are: k₁ = 1.3 × 10⁻¹³T^0.5 exp[ − (1238)/T]; k₂ = 1.5 × 10⁻¹³T^0.5 exp[ − 637/T]; k₃ = 6.6 × 10⁻¹⁴T^0.5 exp[ − 721/T]; k₄ = 1.7 × 10⁻¹³T^0.5 exp[ − 641/T]; k₅ = 9.1 × 10⁻¹⁴T^0.5 exp[ − 157/T]; k₆ = 7.0 × 10⁻¹⁴T^0.50 exp[ − 145/T]. These rate constants are compared with those from previous studies. Some trends in the reactivities are also noted. The globally averaged atmospheric lifetime for methyl chloride, CH₃Cl, with respect to loss by reaction with OH, derived from the rate constant data performed in this study is 1.3 years. The rate constants for the reaction of OH with the other compounds presented in this study are large enough to make these reactions their dominant atmospheric loss pathway.