Pressure dependence of the reaction of chlorine atoms with ethene and acetylene in air at 295 K

The relative rate technique has been used to determine rate constants for the reaction of chlorine atoms with ethene and acetylene over the pressure ranges 10-3000 and 10-5800 Torr, respectively, of synthetic air at 295 K. The decays of the reactants were measured relative to that of either ethane or chloroethane or both. Using a pressure-independent value of 5.7 × 10^-11 cm³ molecule^-1 s^-1 for the reaction of Cl with ethane, the relative data were placed on an absolute basis and fit to the Troe expression with the broadening factor, F, fixed at 0.6. Values of the best-fit low-pressure termolecular rate constant k₀, and high-pressure limiting bimolecular rate constant, k∞, for the reaction of Cl atoms with ethene were k₀₁, = 1.6_-0.3⁺¹ × 10^-29 cm⁶ molecule^-2 s^-1 and k_∞1 = 3.05_-0.4⁺² × 10^-10 cm³ molecule^-1 s^-1, and those for the reaction of Cl atoms with acetylene were k₀₂ = (5.2 ± 0.7) × 10^-30 cm⁶ molecule^-2 s^-1 and k_∞2 = (2.3 ± 0.7) × 10^-10 cm³ molecule^-1 s^-1. Quoted uncertainties reflect statistical (95% confidence) errors and uncertainty in the value of F. The results are discussed with respect to the previous literature data for these reactions and to the chemistry of the upper atmosphere.