Abstract
Rate constants have been measured for the gas-phase reactions of hydroxyl radical with two halons and three of their proposed substitutes and also with CHClBr-CF3 using the discharge-flow-EPR technique over the temperature range 298–460 K. The following Arrhenius expressions have been derived (units are 10−13 cm3 molecule−1 s−1): (9.3−0.9+1.0) exp{−(1326±33)/T} for CHF2Br; (7.2−0.6+0.7) exp{−(1111±32)/T} for CHFBrCF3; (8.5−0.8+0.9) exp{−(1113±35)/T} for CH2BrCF3; (12.8−1.2+1.5) exp{−(995±38)/T} for CHClBrCF3. The rate constants at 298 K have been estimated to be <2×10−17 cm3 molecule−1 s−1 for CF3Br and CF2Br—CF2Br. The atmospheric lifetimes due to hydroxyl attack have been estimated to be 5.5, 3.3, 2.8, and 1.2 years for CHF2Br, CHFBr—CF3, CH2Br—CF3 and CHClBr—CF3, respectively.
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