Atmospheric Chemistry of Tetrachloroethene (Cl2CCCl2): Products of Chlorine Atom Initiated Oxidation

Abstract

The products following Cl atom initiated oxidation of C2Cl4 at 700−760 Torr of air and 230−299 K in the presence and absence of NOx were investigated using three different FTIR smog chamber techniques. There was no measurable effect of temperature on the product yields. CCl3C(O)Cl and COCl2 were formed with molar yields of 68 ± 6% and 77 ± 12% in the presence of NOx and 87 ± 11% and 32 ± 4% in the absence of NOx. These results give branching ratios for the CCl3C(O)Cl and COCl2 forming channels of 0.64 and 0.36 in the presence of NOx and 0.84 and 0.16 in the absence of NOx. Contrary to a recent report by Hasson and Smith (J. Phys. Chem. A, 1999, 103, 2031), variation of the initial C2Cl4 by a factor of 300 over the range (0.016−5.6) × 1014 molecule cm-3 had no discernible effect (<10%) on the product distributions. The different product distribution observed in the presence of NOx may reflect the formation and subsequent decomposition of chemically activated C2Cl5O radicals, formed in the exothermic reaction of C2Cl5O2 with NO. The kinetics of the reaction of Cl atoms with C2Cl4 were measured in 2.0−700 Torr of air at 296 K. The results are in good agreement with the previous study by Nicovich et al. (J. Phys. Chem. 1996, 100, 680). The combined data can be described using Fc = 0.6, ko = (1.8 ± 0.3) × 10-28 cm6 molecule-2 s-1 and k∞ = (4.0 ± 0.4) × 10-11 cm3 molecule-1 s-1. Results are discussed with respect to the atmospheric chemistry of C2Cl4.