Reactions of vinyl radicals at high temperatures: Pyrolysis of vinyl bromide iodide and the reaction H + C2D2 → D + C2HD

Article abstract of DOI:10.1021/j100333a028

Five sets of experiments were carried out to determine the rate constant for dissociation of C₂H₃ at high temperatures. In all cases the measurements involved absorption of H or D Lyman-α radiation in argon-diluted gas mixtures reacting behind shock waves. For pyrolysis of vinyl bromide at 0.5-atm total pressure we found for C₂H₃ + Ar → C₂H₂ + H + Ar, k = 7.0 × 10¹³ exp(-28 kcal/RT) mol^-1 cm³ s^-1 at 1380-1750 K. For the same reaction initiated from vinyl iodide at 0.5-atm total pressure and 1060-1370 K, we found k = 3.5 × 10¹⁴ exp(-33 kcal/RT) mol^-1 cm³ s^-1. In three sets of experiments in which H atoms reacted with C₂D₂ to produce D atoms, we obtained values of k^∞ for the reaction H + C₂H₂ → C₂H₃ of 8 × 10¹¹, 1.2 × 10¹², and 3.4 × 10¹² mol^-1 cm³ s^-1 in the temperature range 1200-1900 K, with no clearly visible temperature dependence. All of the experimental values lie 3-10 times lower than those deduced from earlier work at high temperatures or based on ab initio calculations for the vinyl radical.