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

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 (C 3 H 4 Cl) radical. We measured the continuum spectrum of the 2-chloroallyl radical between 238 and 252 nm and determined the absorption cross section, σ 240 (C 3 H 4 Cl) = (2.5 ± 0.5) × 10 -17 cm 2 . By fitting the C 3 H 4 Cl absorption data to complex kinetic mechanisms, rate coefficients at 298 K were found to be k (Cl+C 3 H 4; 656 Pa, N 2 ) = (1.61 ± 0.27) × 10 -10 cm 3 molecule -1 s -1, k (Cl+C 3 H 4; 670 Pa, He) = (1.34 ± 0.24) × 10 -10 cm 3 molecule -1 s -1, and k (Cl+C 3 H 4; 1330 Pa, He) = (1.75 ± 0. 25) × 10 -10 cm 3 molecule -1 s -1 . The rate coefficient of the self-reaction displayed no pressure dependence between 434 and 1347 Pa in N 2 buffer giving k (C 3 H 4 Cl+C 3 H 4 Cl) = (3.7 ± 1.0) × 10 -11 cm 3 molecule -1 s -1 . A study of the addition reaction of 2-chloroallyl radical and oxygen molecule determined σ 240 (C 3 H 4 ClO 2 ) = (3.6 ± 0.7) × 10 -18 cm 2 and k (O 2 +C 3 H 4 Cl, 705 Pa N 2 ) = (3.6 ± 0.4) × 10 -13 cm 3 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.