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 techniques: 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 CH 2ICl is given (to within ±15%) by the Arrhenius expression k 1 = 4.4 × 10 -11 exp(195/T) cm 3 molecule -1 s -1, which gives k 1 = 8.5 × 10 -11 cm 3 molecule -1 s -1 at 298 K.

Variation of the total pressure of N 2 diluent over the range 5-700 Torr at 295 K had no discernible (<10%) effect on the rate of reaction. At 295 K in 100-700 Torr of N 2 the reaction proceeds via iodine transfer to give CH 2Cl radicals. As part of this work the rate constant k(CH 2Cl+O 2+M) was measured at 295 K in the presence of 1-800 Torr of N 2 diluent.

The results were well described by the Troe expression with a broadening factor F c of 0.6 and limiting low- and high-pressure rate constants of k 0 = (1.8 ± 0.1) × 10 -30 cm 6 molecule -2 s -1 and k ∞ = (3.3 ± 0.3) × 10 -12 cm 3 molecule -1 s -1. The results are discussed with respect to the available literature for reactions of Cl atoms with halogenated organic compounds and the potential role of the title reaction in atmospheric chemistry.