Atmospheric Chemistry of 1,2-Dichloroethane:  UV Spectra of CH₂ClCHCl and CH₂ClCHClO₂ Radicals, Kinetics of the Reactions of CH₂ClCHCl Radicals with O₂ and CH₂ClCHClO₂ Radicals with NO and NO₂, and Fate of the Alkoxy Radical CH₂ClCHClO

A pulse radiolysis technique was used to measure the UV absorption spectra of CH 2 ClCHCl and CH 2 ClCHClO 2 radicals over the range 230−300 nm. At 250 nm, σ(CH 2 ClCHCl) = (1.7 ± 0.2) × 10 -18 and σ(CH 2 ClCHClO 2 ) = (3.5 ± 0.5) × 10 -18 cm 2 molecule -1 . The observed self-reaction rate constant for CH 2 ClCHCl radicals, defined as −d[CH 2 ClCHCl]/d t = 2 k 4 [CH 2 ClCHCl] 2 was k 4 = (2.0 ± 0.3) × 10 -11 cm 3 molecule -1 s -1 . The rate constant for reaction of CH 2 ClCHCl radicals with O 2 in one bar of SF 6 diluent was (2.4 ± 0.3) × 10 -12 cm 3 molecule -1 s -1 . The rate constants for the reactions of CH 2 ClCHClO 2 radicals with NO and NO 2 were k 5 ≥ 9 × 10 -12 and k 6 = (9.8 ± 0.6) × 10 -12 cm 3 molecule -1 s -1, respectively. The rate constant for the reaction of F atoms with CH 2 ClCH 2 Cl was k 3 = (2.6 ± 0.2) × 10 -11 cm 3 molecule -1 s -1 . The reaction of CH 2 ClCHClO 2 radicals with NO produced NO 2 and, by implication, CH 2 ClCHClO radicals. A FTIR spectroscopic technique showed that CH 2 ClCHClO radicals undergo both reaction with O 2 and decomposition via intramolecular 3-center HCl elimination. In 700 Torr of air at 296 K the rate constant ratio k O 2 / k decomp = (2.3 ± 0.2) × 10 -20 cm 3 molecule -1 . A lower limit of 4 × 10 5 s -1 was deduced for the rate of intramolecular 3-center HCl elimination from CH 2 ClCHClO radicals at 296 K in 1 bar of SF 6 diluent. As part of this work a relative rate technique was used to measure rate constants of (1.3 ± 0.2) × 10 -12 and (6.4 ± 1.4) × 10 -14 cm 3 molecule -1 s -1 for the reactions of Cl atoms with CH 2 ClCH 2 Cl and CH 2 ClC(O)Cl, respectively. All experiments were performed at 296 K. Results are discussed in the context of the atmospheric chemistry of 1,2-dichloroethane.