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

Abstract

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 persistent addition 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, σ240(C3H4Cl) = (2.5 ± 0.5) × 10-17 cm2. By fitting the C3H4Cl absorption 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 molecule-1 s-1, k(Cl+C3H4; 670 Pa, He) = (1.34 ± 0.24) × 10-10 cm3 molecule-1 s-1, and k(Cl+C3H4; 1330 Pa, He) = (1.75 ± 0. 25) × 10-10 cm3 molecule-1 s-1. The rate coefficient of the self-reaction displayed no pressure dependence between 434 and 1347 Pa in N2 buffer giving k(C3H4Cl+C3H4Cl) = (3.7 ± 1.0) × 10-11 cm3 molecule-1 s-1. A study of the addition reaction of 2-chloroallyl radical and oxygen molecule determined σ240 (C3H4ClO2) = (3.6 ± 0.7) × 10-18 cm2 and k(O2+C3H4Cl, 705 Pa N2) = (3.6 ± 0.4) × 10-13 cm3 molecule-1 s-1. The listed uncertainties denote two standard deviations, and those for rate coefficients include the uncertainty of the appropriate absorption cross section.