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

Abstract

Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C 2HCl 3 ( k 1) and C 2Cl 4 ( k 2) over an extended temperature 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 adequately describes the low temperature data for k 1 (<650 K) and the entire data set for k 2 and is given by (in units of cm 3 molecule −1 s −1): k 1(291−650 K )=(9.73±1.15)×10 −13 exp (158.7±44.0)/T, k 2(293−720 K )=(1.53±0.14)×10 −12 exp (−688.2±67.5)/T. Error limits are 2 σ values. The room temperature values for k 1 and k 2 are within ±2 σ 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 state theory calculations infer an OH addition mechanism. The lack of a measurable kinetic isotope effect for k 1 is consistent with this mechanism. Insight into the subsequent reactions of the chemically activated intermediate are presented in the form of potential energy diagrams derived from ab initio calculations.