A VUV photoionization study of the multichannel reaction of phenyl radicals with 1,3-butadiene under combustion relevant conditions

We studied the reaction of phenyl radicals (C6H5) with 1,3-butadiene (H2CCHCHCH2) exploiting a high temperature chemical reactor under combustion-like conditions (300 Torr, 873 K). The reaction products were probed in a supersonic beam by utilizing VUV radiation from the Advanced Light Source and by recording the experimental PIE curves at mass-to-charge ratios of m/z = 130 (C10H10+), 116 (C9H8+), and 104 (C8H8+). Our data suggest that the atomic hydrogen (H), methyl (CH3), and vinyl (C2H3) losses are open with estimated branching ratios of about 86 +/- 4%, 8 +/- 2%, and 6 +/- 2%, respectively. The isomer distributions were probed further by fitting the experimentally recorded PIE curves with a linear combination of the PIE curves of individual C10H10, C9H8, and C8H8 isomers. These fits indicate the formation of three C10H10 isomers (trans-1,3-butadienylbenzene, 1,4-dihydronaphthalene, 1-methylindene), three C9H8 isomers (indene, phenylallene, 1-phenyl-1-methylacetylene), and a C8H8 isomer (styrene). A comparison with results from recent crossed molecular beam studies of the 1,3-butadiene-phenyl radical reaction and electronic structure calculations suggests that trans-1,3-butadienylbenzene (130 amu), 1,4-dihydronaphthalene (130 amu), and styrene (104 amu) are reaction products formed as a consequence of a bimolecular reaction between the phenyl radical and 1,3-butadiene. 1-Methylindene (130 amu), indene (116 amu), phenylallene (116 amu), and 1-phenyl-1-methylacetylene (116 amu) are synthesized upon reaction of the phenyl radical with three C4H6 isomers: 1,2-butadiene (H2CCCH(CH3)), 1-butyne (HCCC2H5), and 2-butyne (CH3CCCH3); these C4H6 isomers can be formed from 1,3-butadiene via hydrogen atom assisted isomerization reactions or via thermal rearrangements of 1,3-butadiene involving hydrogen shifts in the high temperature chemical reactor.