Kinetic and Modeling Studies of the Reaction of Hydroxyl Radicals with Tetrachloroethylene

Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C2Cl4 (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 cm3 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.