FTIR SPECTROSCOPIC STUDIES OF THE MECHANISMS OF THE HALOGEN ATOM INITIATED OXIDATION OF HALOACETALDEHYDES

Product studies of Cl atom initiated oxidation of ClCH2CHO and Br atom initiated oxidation of BrCH2CHO were conducted by FTIR spectroscopy a t 297 +/- 2 K in 700 Torr of O-2/N-2 diluent, using reactant partial p ressures in both the torr and millitorr ranges. The halogen atoms init iate reaction via hydrogen abstraction from the aldehydic group (CHO), producing haloacetyl radicals, XCH(2)CO, where X = Cl or Pr. In 700 T orr of air, the XCH(2)CO radicals may react via three channels: (i) O- 2-addition, XCH(2)CO + O-2 --> XCH(2)C(O)O-2; (ii) unimolecular dissoc iation by C-C bond cleavage, XCH(2)CO (+M) --> XCH(2) + CO (+M); and ( iii) unimolecular dissociation by C-X bond cleavage, XCH(2)CO (+M) --> X + CH2C=O (+M). All three channels were observed for BrCH,CO radical s, enabling estimation of the branching ratios, but ClCH2CO reacts onl y by O-2-addition. Subsequent reactions of XCH(2)C(O)O-2 radicals lead to XCH(2)O radical and CO2 formation. The ClCH2O radical reacts with O-2 to produce CHClO and HO2, while the BrCH2O radical mainly eliminat es the Pr atom, based on CH2O detected.