EVIDENCE FOR THE 3-CENTER ELIMINATION OF HCL FROM CH3CHCLO

Time-resolved IR spectral photography and transient diode laser absorption measurements reveal a yield of HCl from the photolysis of Cl2 in the presence of C2H5Cl and O2 which is 78% larger than expected from Cl + C2H5Cl. The HCl formation occurs in two steps: a rapid rise to [HCl] = [Cl]0, followed by a secondary rise to [HCl] = 1.78[Cl]0 with a rate constant of k3 = (5.2 +/- 1.3) X 10(-12) cm3 S-1. In the presence of NO, the rate of secondary HCl formation is greatly enhanced, but its yield (84%) is comparable to that in the absence of NO. The secondary HCl is explained as an elimination product from the CH3CHClO, which can be generated by the reaction of CH3CHClO2 with itself or with NO. The fact that the secondary HCl yield increases by 12% when using CD3CH2Cl shows that the secondary HCl is formed mainly by three-center elimination from the 1-chloroethoxy radical. We also report UV absorption cross sections for CH3CHClO2, which has a broad maximum of sigma(max) = 0.029 angstrom2 from 215 to 248 nm, and CH2ClCH2O2, with sigma(max) = 0.045 angstrom2 at 240 nm. The self-reaction rate constants are (5.2+/-1.3) X 10(-12) cm3 s-l and (6.04-0.8) X 10(-12) cm3 s-1, respectively. Finally, the rate constant for the reaction Cl + C2H5Cl = C2H4Cl + HCl (1) is determined to be k1 = (7.3 +/- 0.9) X 10(-12) cm3 s-1.