Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with 1,1-dichloroethylene (k 1 ) and trans-1,2-dichloroethylene (k 2 ) over an extended temperature range at 740 ( 10 Torr in a He bath gas. Absolute rate measurements were obtained using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. Rate measurements for k 1 exhibited complex behavior with negative temperature dependence at temperatures below 640 K, a rapid falloff in rate between 650 and 700 K, and positive temperature dependence from 700 to 750 K. The simple Arrhenius equation adequately describes the data below 640 K and above 700 K and is given (in units of cm 3 molecule -1 s -1 ) by k 1 (291-640 K) ) (1.81 ( 0.36) × 10 -12 exp(511 ( 71)/T and k 1 (700-750 K) ) 3.13 × 10 -10 exp(-5176/T). Rate measurements for k 2 also exhibited complex behavior with a near-zero or slightly negative temperature dependence below 500 K and a near-zero or slightly positive temperature dependence above 500 K. The modified Arrhenius equation adequately describes all of the data and is given (in units of cm 3 molecule) by k 2 (293-720 K) ) (9.75 ( 1.14) × 10 -18 T 1.73( 0.05 exp(727 ( 46)/T. Error limits are 2σ values. The room-temperature values for k 1 and k 2 are within (2σ of previous data using different techniques. The rate measurements were modeled using QRRK theory. OH addition to the unsubstituted carbon followed by adduct stabilization describes the low-temperature measurements for k 1 . Analysis of equilibration in this system yields a C-O bond dissociation enthalpy of 32.8 ( 1.5 kcal mol -1 at 298 K, a value confirmed by ab initio calculations. OH addition followed by Cl elimination described the experimental data for k 2 . Ab initio based transition state calculations for the H atom abstraction channel indicated that this mechanism is consistent with the rate measurements for k 1 above 700 K. The H abstraction channel for k 2 could not be observed because of the presence of a more rapid Cl elimination channel at elevated temperatures. H abstraction is predicted to be the dominant reaction channel for both k 1 and k 2 at flame temperatures.

The kinetics of the title reaction were investigated between 293 and 730 K at 740 ( 10 Torr in a helium bath gas. Absolute rate measurements were obtained using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. Rate coefficients exhibited complex behavior with negative temperature dependence at temperatures below 560 K, a rapid drop in rate between 560 and 620 K, and a positive temperature dependence above 620 K. The simple Arrhenius equation adequately describes the data at and below 560 K and is given by (in units of cm 3 molecule -1 s -1 ) k(293-560 K) ) (2.72 ( 0.35) × 10 -12 exp(335 ( 42)/T. Error limits are 2σ values. The low-temperature values for k are within (2σ of the most recent measurements of this reaction obtained under atmospheric pressure conditions. Above 620 K, our measurement combined with the recent measurements of Liu et al. 8 to yield the following rate expression: k(620-1173 K) ) (6.3 ( 4.0) × 10 -11 exp(-2740 ( 490)/T. Error limits are 2σ values. The rate data were interpreted using variational transition state theory and QRRK theory. OH addition to the site followed by adduct stabilization describes the low-temperature measurements. Ab initio-based transition state calculations for the H abstraction channel indicated that this mechanism is consistent with the rate measurements above 620 K. H abstraction is predicted to be the dominant reaction channel above temperatures of 800 K.