Atmospheric chemistry of (Z)- and (E)-1,2-dichloroethene: kinetics and mechanisms of the reactions with Cl atoms, OH radicals, and O-3

Smog chambers interfaced with in situ FT-IR detection were used to investigate the kinetics and mechanisms of the Cl atom, OH radical, and O-3 initiated oxidation of (Z)- and (E)-1,2-dichloroethene (CHCl=CHCl) under atmospheric conditions. Relative and absolute rate methods were used to measure k(Cl + (Z)-CHCl=CHCl) = (8.80 +/- 1.75) x 10(-11), k(Cl + (E)-CHCl=CHCl) = (8.51 +/- 1.69) +/- 10(-11), k(OH + (Z)-CHCl=CHCl) = (2.02 +/- 0.43) 10(-12), k(OH + (E)-CHCl=CHCl) = (1.94 +/- 0.43) 10(-12), k(O-3 + (Z)-CHCl=CHCl) = (4.50 +/- 0.45) x 10(-21), and k(O-3 + (E)-CHCl=CHCl) = (1.02 +/- 0.10) x 10(-19) cm(3) molecule(-1) s(-1) in 700 Torr of N-2/air diluent at 298 +/- 2 K. Pressure dependencies for the Cl atom reaction kinetics were observed for both isomers, consistent with isomerization occurring via Cl atom elimination from the chemically activated CHCl-CHCl-Cl adduct. The observed products from Cl initiated oxidation were HC(O)Cl (117-133%), CHCl2CHO (29-30%), and the corresponding CHCl=CHCl isomer (11-20%). OH radical initiated oxidation gives HC(O)Cl as a major product. For reaction of OH with (E)-CHCl=CHCl, (Z)-CHCl=CHCl was also observed as a product. A significant chlorine atom elimination channel was observed experimentally (HCl yield) and supported by computational results. Photochemical ozone creation potentials of 12 and 11 were estimated for (Z)- and (E)-CHCl=CHCl, respectively. Finally, an empirical kinetic relationship is explored for the addition of OH radicals or Cl atoms to small alkenes. The results are discussed in the context of the atmospheric chemistry of (Z)- and (E)-CHCl=CHCl.