KINETICS AND MECHANISM OF THE GAS-PHASE REACTION OF ATOMIC CHLORINE WITH CH2ICL AT 206-432 K

The title reaction was studied using two different experimental techni ques: laser flash photolysis with resonance fluorescence detection of Cl atoms and continuous photolysis with FTIR detection of end products . Over the temperature range 206-432 K the rate constant for reaction of Cl atoms with CH2ICl is given (to within +/-15%) by the Arrhenius e xpression k(1) = 4.4 x 10(-11) exp(195/T) cm(3) molecule(-1) s(-1), wh ich gives k(1) = 8.5 x 10(-11) cm(3) molecule(-1) s(-1) at 298 K. Vari ation of the total pressure of N-2 diluent over the range 5-700 Torr a t 295 K had no discernible (<10%) effect on the rate of reaction. At 2 95 K in 100-700 Torr of N-2 the reaction proceeds via iodine transfer to give CH2Cl radicals. As part of this work the rate constant k(CH2Cl +O-2+M) was measured at 295 K in the presence of 1-800 Torr of N-2 dil uent. The results were well described by the Tree expression with a br oadening factor F-c of 0.6 and limiting low-and high-pressure rate con stants of k(0) = (1.8 +/- 0.1) x 10(-30) cm(6) molecule(-2) s(-1) and k(infinity) = (3.3 +/- 0.3) x 10(-12) cm(3) molecule(-1) s(-1). The re sults are discussed with respect to the available literature for react ions of CI atoms with halogenated organic compounds and the potential role of the title reaction in atmospheric chemistry.