ATMOSPHERIC CHEMISTRY OF 1,2-DICHLOROETHANE - UV SPECTRA OF CH2CLCHCLAND CH2CLCHCLO2 RADICALS, KINETICS OF THE REACTIONS OF CH2CLCHCL RADICALS WITH O-2 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 spe ctra of CH2ClCHCl and CH2ClCHClO2 radicals over the range 230-300 nm. At 250 nm, sigma(CH2ClCHCl) = (1.7 +/- 0.2) x 10(-18) and sigma(CH2ClC HClO2) = (3.5 +/- 0.5) x 10(-18) cm(2) molecule(-1). The observed self -reaction rate constant for CH2ClCHCl radicals, defined as -d[CH2ClCHC l]/dt = 2k(4)[CH2ClCHCl](2) was k(4) = (2.0 +/- 0.3) x 10(-11) cm(3) m olecule(-1) s(-1). The rate constant for reaction of CH2ClCHCl radical s with O-2 in one bar of SF6 diluent was (2.4 +/- 0.3) x 10(-12) cm(3) molecule(-1) s(-1). The rate constants for the reactions of CH2ClCHCl O2 radicals with NO and NO2 were k(5) greater than or equal to 9 X 10( -12) and k(6) = (9.8 +/- 0.6) x 10(-12) cm(3) molecule(-1) s(-1), resp ectively. The rate constant for the reaction of F atoms with CH2ClCH2C l was k(3) = (2.6 +/- 0.2) x 10(-11) cm(3) molecule(-1) s(-1). The rea ction of CH2ClCHClO2 radicals with NO produced NO2 and, by implication , CH2ClCHClO radicals. A FTIR spectroscopic technique showed that CH2C lCHClO radicals undergo both reaction with O-2 and decomposition via i ntramolecular 3-center HCl elimination. In 700 Torr of air at 296 K th e rate constant ratio k(O2)/k(decomp) = (2.3 +/- 0.2) x 10(-20) cm(3) molecule(-1). A lower limit of 4 x 10(5) s(-1) was deduced for the rat e of intramolecular 3-center HCl elimination from CH2ClCHClO radicals at 296 K in 1 bar of SF6 diluent. As part of this work a relative rate technique was used to measure rate constants of (1.3 +/- 0.2) x 10(-1 2) and (6.4 +/- 1.4) x 10(-14) cm(3) molecule(-1) s(-1) for the reacti ons of Cl atoms with CH2ClCH2Cl and CH2ClC(O)Cl, respectively. All exp eriments were performed at 296 K. Results are discussed in the context of the atmospheric chemistry of 1,2-dichloroethane.