TIME-RESOLVED STUDIES OF INTERMEDIATE PRODUCTS IN THE OXIDATION OF HCFC 141B (CFCL2CH3) AND HCFC 142B (CF2CLCH3)

The oxidative degradation of HCFC 141b (CFCl2CH3) and HCFC 142b (CF2Cl CH3) in the presence of NO at T = 293 K and p = 50 mbar has been studi ed using laser pulse initiation combined with cw laser long path absor ption/LiF for the detection of OH and NO2. The absolute yield and temp oral behaviour of these products have been found to be sensitive indic ators for the reaction behaviour of the alkoxy radicals CFCl2CH2O and CF2ClCH2O, respectively. The rate coefficients for the reactions of th e alkoxy radicals with O-2 were determined 2 to be k(CFCl2CH2O + O-2-- >CFCl2CHO + HO2) = (2.0+/-1.0)x10(-15) cm(3)/s and k(CF2ClCH2O + O-2-- >CF2ClCHO + HO2) = (2.5+/-1.5)x10(-15) cm(3)/s. Upper limits for the r ate coefficients for unimolecular decomposition of the alkoxy radicals by C-C-bond fission of k(CFCl2CH2O + M-->CFCl2 + CH2O + M)less than o r equal to 1.0x10(3) s(-1) and k(CF2ClCH2O + M-->CF2Cl + CH2O + M)less than or equal to 1.5x10(3) s(-1) were derived. We conclude from these data that CFCl2CHO and CF2ClCHO will be formed as the dominant primar y carbonyl products in the oxidation of HCFC 141b and 142b throughout the troposphere. Moreover, the rate coefficients for the reactions of the HCFCs with OH radicals at T = 293 K have been measured. The values k(CFCl2CH3 + OH-->CFCl2CH2 + H2O) = (4.6+/-0.8)x10(-15) cm(3)/s and k (CF2ClCH3 + OH-->CF2ClCH2 + H2O) = (2.6+/-0.4)x10(-15) cm(3)/s were ob tained.