Kinetic studies of the reaction of hydroxyl radicals with trichloroethylene and tetrachloroethylene

Rate coefficients are reported for the gas-phase reaction of the hydroxyl r adical (OH) with C2HCl3 (k(1)) and C2Cl4 (k(2)) over an extended temperatur e range at 740+/-10 Torr in a He bath gas. These absolute rate measurements were accomplished using a laser photolysis/laser-induced fluorescence (LP/ LIF) technique under slow flow conditions. The simple Arrhenius equation ad equately describes the low temperature data for k(1) (<650 K) and the entir e data set for k(2) and is given by tin units of cm(3) molecule(-1) s(-1)): k(1)(291 - 650 K) = (9.73 +/- 1.15) x 10(-13) exp(158.7 +/- 44.0)/T, k(2)(293 - 720 K) = (1.53 +/- 0.14) x 10(-12) exp (-688.2 +/- 67.5)/T. Error limits are 2<sigma> values. The room temperature values for k(1) and k(2) are within +/-2 sigma of previous data using different techniques. The Arrhenius activation energies for k(1) and k(2) are a factor of 2-3 lower than previously reported values. The experimental measurements for both k(1 ) and k(2) in conjunction with transition state and variation transition st ate theory calculations infer an OH addition mechanism. The lack of a measu rable kinetic isotope effect for k(1) is consistent with this mechanism. In sight into the subsequent reactions of the chemically activated intermediat e are presented in the form of potential energy diagrams derived from ab in itio calculations. (C) 2001 Elsevier Science Ltd. All rights reserved.