A VUV photoionization study of the combustion-relevant reaction of the phenyl radical (C ₆H ₅) with propylene (C ₃H ₆) in a high temperature chemical reactor

We studied the reaction of phenyl radicals (C ₆H ₅) with propylene (C ₃H ₆) exploiting a high temperature chemical reactor under combustion-like conditions (300 Torr, 1200-1500 K). The reaction products were probed in a supersonic beam by utilizing tunable vacuum ultraviolet (VUV) radiation from the Advanced Light Source and recording the photoionization efficiency (PIE) curves at mass-to-charge ratios of m/z = 118 (C ₉H ₁₀ ⁺) and m/z = 104 (C ₈H ₈ ⁺). Our results suggest that the methyl and atomic hydrogen losses are the two major reaction pathways with branching ratios of 86 ± 10% and 14 ± 10%. The isomer distributions were probed by fitting the recorded PIE curves with a linear combination of the PIE curves of the individual C ₉H ₁₀ and C ₈H ₈ isomers. Styrene (C ₆H ₅C ₂H ₃) was found to be the exclusive product contributing to m/z = 104 (C ₈H ₈ ⁺), whereas 3-phenylpropene, cis-1-phenylpropene, and 2-phenylpropene with branching ratios of 96 ± 4%, 3 ± 3%, and 1 ± 1% could account for the signal at m/z = 118 (C ₉H ₁₀ ⁺). Although searched for carefully, no evidence of the bicyclic indane molecule could be provided. The reaction mechanisms and branching ratios are explained in terms of electronic structure calculations nicely agreeing with a recent crossed molecular beam study on this system.