High Temperature Reactions of Phenylacetylene

Hydrogen atom abstraction from phenylacetylene (C6H5‐C2H) like its reaction with hydrogen atoms have been studied at elevated temperatures behind reflected shocks. ‐ The unimolecular decomposition of very low initial concentrations (3 ‐ 22 ppm) of phenylacetylene was investigated in the temperature range 1600 to 1900 K by monitoring the temporal H‐atom production. ‐ For C6H5‐C2H + H, the thermal decomposition of very low concentrations (1 ‐ 3 ppm) of C2H5I served as H‐atom source. Atomic resonance absorption spectrometry (ARAS) was used to record simultaneously H‐atom and I‐atom profiles. The experiments covered the temperature range 1190 to 1530 K. ‐ For both series of experiments, the total pressure was about 2.3 (+/‐0.3) bar. For the unimolecular reaction R1: C6H5‐C2H → C6H4‐C2H + H a rate constant expression of: magnified image was found. For the bimolecular reaction R2: C6H5‐C2H + H → products a rate constant of: magnified image was deduced. From the available thermochemical data two product channels have to be discussed: magnified image Detailed evaluation of existing thermodynamic data enables the calculation of an equilibrium constant for reaction R 2a. From this and under the assumption that reaction R 2a is the dominant product pathway at elevated temperatures, a rate constant expression of magnified image is deduced for the reaction of phenyl readicals with acetylene, which is an important process in sooting flames: magnified image This rate constant agrees within a factor of 2 with the data from recent studies executed by Fahr et al. [1a, 1b].