Kinetics and thermochemistry of the addition of atomic chlorine to acetylene

Atomic Cl was generated by pulsed laser photolysis at 193 nm of CCl 4, and was monitored by time resolved resonance fluorescence in the course of reaction with excess C 2H 2, diluted in Ar bath gas at pressures from 13 to 800 mbar. At 288 K simple pseudo first order kinetics were observed. Over 365–430 K bi-exponential decays were obtained, because of equilibration between the β-chlorovinyl adduct and the reactants. The ratios of forward and reverse rate constants yield Δ f H 298( CH CHCl) = 274.0 ± 1.0 kJ mol −1 via a Third-Law analysis of the carbon–chlorine bond strength. The thermochemistry compares well with that predicted by an initio theory. The effective second-order rate constant was pressure dependent and was analyzed using Troe’s unimolecular formalism. Over the whole temperature range the low-pressure limiting value for addition, with Ar bath gas, is given by k 0 = 4.1 × 10 −30 ( T/300 K) −2.47 cm 6 molecule −2 s −1.