Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C 2 Cl 4 (k 1 ) over an extended temperature range at 740 ( 10 Torr in a He bath gas. These absolute rate measurements were conducted using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. The lower temperature values for k 1 are within (2σ of previous data using different techniques. The overall slope of our Arrhenius plot varies slightly from previously reported values. Agreement within our own data holds up to ∼720 K, but reliable measurement beyond this temperature was hampered by apparent thermal decomposition of our OH source (HONO). An Arrhenius fit to the data yielded the expression k 1 (T) ) (1.68 ( 0.25) × 10 -12 exp(-764.2 ( 79.1/T), whereas a three-parameter Arrhenius fit yielded the expression k 1 (T) ) (1.93 ( 0.20) × 10 -22 (T) 3.2 exp(660.8 ( 54.6/T), where k is in units of cm 3 molecule -1 s -1 . This work shows some deviation from previous low-temperature data. We propose that surface absorption influenced previously measured rate constants. Significant absorption was evident at low temperatures, and an experimental technique was developed to negate this effect. The predicted mechanisms were conceptualized using ab initio calculations to define the activated complex and transient intermediates, and thus predict the most likely path and products. Quantum RRK analysis yielded no overall pressure dependence. Model predictions indicate that trichloroethenol formation via Cl elimination dominates up to temperatures of 2000 K. At flame temperatures, the analysis also predicts increased formation of trichloroacetyl chloride with hydrogen elimination and back reaction to the original reactants.

Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C 2 Cl 4 (k 1 ) over an extended temperature range at 740 ( 10 Torr in a He bath gas. These absolute rate measurements were conducted using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. The lower temperature values for k 1 are within (2σ of previous data using different techniques. The overall slope of our Arrhenius plot varies slightly from previously reported values. Agreement within our own data holds up to ∼720 K, but reliable measurement beyond this temperature was hampered by apparent thermal decomposition of our OH source (HONO). An Arrhenius fit to the data yielded the expression k 1 (T) ) (1.68 ( 0.25) × 10 -12 exp(-764.2 ( 79.1/T), whereas a three-parameter Arrhenius fit yielded the expression k 1 (T) ) (1.93 ( 0.20) × 10 -22 (T) 3.2 exp(660.8 ( 54.6/T), where k is in units of cm 3 molecule -1 s -1 . This work shows some deviation from previous low-temperature data. We propose that surface absorption influenced previously measured rate constants. Significant absorption was evident at low temperatures, and an experimental technique was developed to negate this effect. The predicted mechanisms were conceptualized using ab initio calculations to define the activated complex and transient intermediates, and thus predict the most likely path and products. Quantum RRK analysis yielded no overall pressure dependence. Model predictions indicate that trichloroethenol formation via Cl elimination dominates up to temperatures of 2000 K. At flame temperatures, the analysis also predicts increased formation of trichloroacetyl chloride with hydrogen elimination and back reaction to the original reactants.

Rate coe cients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C 2 HCl 3 (k 1 ) and C 2 Cl 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¯uorescence (LP/LIF) technique under slow¯ow 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 À1 s À1 ):Error limits are 2r values. The room temperature values for k 1 and k 2 are within 2r of previous data using di erent 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 e ect 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. Ó