FTIR PRODUCT STUDY OF THE CL-INITIATED OXIDATION OF CH3CL - EVIDENCE FOR HCL ELIMINATION FROM THE CHLOROMETHOXY RADICAL

The Cl-atom-initiated oxidation of CH3Cl has been investigated at 296 K by UV irradiation of mixtures of CH3Cl, Cl-2, and O-2 in Na The obse rved products, measured using Fourier transform infrared (FTIR) spectr oscopy, are HC(O)Cl, CO, HCl, and CH2ClOOH. The ratio HC(O)Cl/CO (R) i s directly related to the O-2 pressure (1-147 Torr). The HCl yield is inversely related to the O-2 pressure. At 1 Torr O-2, the CO yield is >60%, while the HCl yield is 155%. We interpret these data as evidence for a competition between the decomposition and O-2 reactions of the CH2ClO radical: CH2ClO --> HCO + HCl (ks); CH2ClO + O-2 --> HC(O)Cl HO2(k(6)) The first reaction involves a three-center molecular elimina tion of HCl, observed previously for 1-chloroethoxy radicals. The rati o R is inversely related to the total pressure (12-700 Torr), indicati ng that the first reaction is in the falloff regime. The ratio k(6)/k( 8) was determined to be 5.0 x 10(-18) cm(3)/molecule at 700 Torr total pressure. We have also measured the rate constant ratio for reaction of HCO with Cl-2 (k(11)) and O-2 (kg) to be k(11)/k(9) = 1.15 (+/-0.12 ). This ratio agrees with that derived from literature values of these rate constants, verifying that the HCO radical is present during the oxidation process.