Chlorination chemistry. I. Rate coefficients, reaction mechanisms, and spectra of the chlorine and bromine adducts of propargyl halides

Cavity ring-down spectroscopy (CRDS), end-product analysis, and ab initio c alculations have determined absorption cross sections, rate coefficients, r eaction mechanisms, and thermochemistry relevant to the addition of halogen atoms to propargyl chloride and propargyl bromide. Halogen atoms were prod uced by laser photolysis, and the addition reaction products were probed at a variable delay by CRDS using a second laser pulse. We report the continu um spectra of C3H3Cl2 (1,2-dichloroallyl), C3H3ClBr (1-chloro-2-bromoallyl) , and C3H3Br2 (1,2-dibromoallyl) radicals between 238 and 252 nm and the ab sorption cross sections, sigma(240)(C3H3Cl2) = (4.20 +/- 1.05) x 10(-17) cm (2) molecule(-1) and sigma(242)(C3H3Br2) = (1.04 +/- 0.31) X 10(-17) cm(2) molecule(-1). When the observed data are fit to complex reaction schemes, t he 298 K rate coefficients for formation of 1,2-dihaloallyl radicals at 665 Pa were found to be k(Cl + C3H3Cl) = (1.2 +/- 0.2) x 10(-10) cm(3) molecul e(-1) s(-1) and k(Br + C3H3Br) = (2 +/- 1) x 10(-12) cm(3) molecule(-1) s(- 1). At 298 K and 665 Pa the self-reaction rate coefficients of these radica ls were found to be k(C3H3Cl2 + C3H3Cl2) = (3.4 +/- 0.9) x 10(-11) cm(3) mo lecule(-1) s(-1) and k(C3H3Br2 + C3H3Br2) = (1.7 +/- 1.1) x 10(-11) cm(3) m olecule(-1) s(-1). The listed uncertainties are twice the standard deviatio n of individual determinations, and those for rate coefficients include the uncertainty of the appropriate absorption cross section.