The flash photolysis resonance fluorescence technique has been utilized to determine the Arrhenius parameters for several reactions between the hydroxyl radical and halogenated hydrocarbons. The reactions studied, and their corresponding Arrhenius expressions in units of cm3 molecule™1 s 1 are shown: (1) OH + CH2C1F -CHC1F + H20, ki = (2.84 ± 0.3) X 10™12 exp(-(1259 ± 50)/T) K; (2) OH + CHC12F -CC12F + H20, k2 = (1.87 ± 0.2) X 10 12 exp(-(1245 ± 26)/T) (245-375) K; (3) OH + CHC1F2 -» CC1F2 + H20, k3 = (9.25 ± 1.0) X 10™13 exp(-(1575 ± 71 )/T) (250-350) K; (4) OH + CH3CCI3 -CH2CC13 + H20, fc4 = (3.72 ± 0.4) X 10™12 exp(-(1627 ± 50)/T) (260-375) K; (5) OH + CH3CF2C1 -> CH2CF2C1 + H20, h = (1.15 ± 0.15) X 10™12 exp(-(1748 ± 30)/T) (273-375) K; (6) OH + CF2C1CFC12 -products, k6 < 3 X 10 16. Tropospheric lifetimes have been calculated for the above species by combining the rate constant data with global seasonally and diurnally averaged hydroxyl radical concentrations.
Reported in this study are temperature dependent rate data for the reaction of OH with the partially halogenated methane species CH3Cl, CH2Cl2, CHCl3, and CH3Br. The nominal temperature range covered was 245–375 K. The appropriate Arrhenius expressions are kA= (1.84±0.18) ×10−12 exp[−(2181±70/RT)], kB= (4.27±0.63) ×10−12 exp[−(2174±161/RT)], kC= (4.69±0.71) ×10−12 exp[(2254±214/RT)], kD= (7.93±0.79) ×10−13 exp[−(1766±116/RT)]. Units are cm3 molecule−1⋅s−1. No simple correlations between Eact and C–H bond strengths were found. The impact of these halogenated species on stratospheric ozone is also discussed.
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