Chlorination Chemistry 2. Rate Coefficients, Reaction Mechanism, and Spectrum of the Chlorine Adduct of Allene

Dean B. Atkinson* and Jeffrey W. Hudgens, in press.

Cavity ring-down (CRD) spectroscopy and ab initio calculations have determined the reaction rate coefficients, mechanism, and thermochemistry relevant to the addition of a chlorine atom to allene. Chlorine atoms were produced by laser photolysis at 351 nm and the addition reaction products were probed at a variable delay by CRD spectroscopy using a second laser pulse. Ab initio results indicate that the only product is the 2-chloroallyl (C3H4Cl) radical. We measured the continuum spectrum of the 2-chloroallyl radical between 238 and 252 nm and determined the absorption cross-section, s 240(C3H4Cl) = (2.5 ± 0.5) ´ 10-17 cm2 molec-1. By fitting the observed data to complex kinetic mechanisms, rate coefficients at 298 K were found to be k(Cl + C3H4; 656 Pa, N2) = (1.61 ± 0.27) ´ 10-10 cm3 molec-1 s-1, k(Cl + C3H4; 670 Pa, He) = (1.34 ± 0.24) ´ 10-10 cm3 molec-1 s-1, and k(Cl + C3H4; 1330 Pa, He) = (1.75 ± 0. 25) ´ 10-11 cm3 molec-1 s-1. The recombination reaction displayed no pressure dependence between 434 Pa and 1347 Pa in N2 buffer giving k(C3H4Cl + C3H4Cl) = (3.7 ± 1.0) ´ 10-11 cm3 molec-1 s-1. A study of the addition reaction of 2-chloroallyl radical and oxygen molecule determined s 240(C3H4ClO2) = (3.6 ± 0.7) ´ 10-18 cm2   molec-1 and k(O2 + C3H4Cl, 705 Pa N2) = (3.5 ± 0.5) ´ 10-13 cm3 molec-1 s-1. Quoted uncertainties denote two standard deviations and include the propagated uncertainties of absorption cross-sections.

*National Research Council postdoctoral associate/NIST.