Kinetics and Thermochemistry of C2H3 and CH2CCl Radicals: Study of the C2H3 + HCl = C2H4 + Cl and CH2CCl + HCl = C2H3Cl + Cl Reactions

Article abstract of DOI:10.1021/j100350a032

The kinetics of the reactions of C2H3 and CH2CCl radicals with HCl have been studied in a tubular flow reactor coupled to a photoionization mass spectrometer in the temperature range 298-495 K.Each radical was produced by the pulsed homogeneous photolysis of a suitable precursor using an excimer laser.Radical decay and product growth profiles were monitored in time-resolved experiments.The Arrhenius rate expression obtained from the measured C2H3 + HCl rate constants is 6.6 (+/- 1.0) x 10^-13 exp(670 (+/- 230) cal mol^-1/RT) cm³ molecule^-1 s^-1.The heat of formation (67.1 (+/- 0.6) kcal mol^-1) and entropy (55.9 (+/- 2.6) cal mol^-1 K^-1) of C2H3 were determined from this kinetic information on the C2H3 + HCl reaction together with recently measured rate constants for the Cl + C2H4 reaction.A Third Law treatment of the same data using a calculated entropy yields essentially the same heat of formation (66.9 (+/- 0.3) kcal mol^-1) but with reduced uncertainty limits.The rate constant for the CH2CCl + HCl reaction was found to be temperature independent, having an average value over the temperature range covered of 2.2 (+/- 0.3) x 10^-13 cm³ molecule^-1 s^-1.This result was used to obtain a lower limit for the CH2CCl heat of formation of 60 (+/- 0.3) kcal mol^-1.The reduced reactivity caused by chlorine substitution at the radical site is briefly discussed.