Forming benzene in flames by chemically activated isomerization

TLDR: In this article, the authors showed that benzene is not formed in flames by high-pressure-limit addition reactions, as had been implied previously, but by chemically activated addition and isomerization reactions.

Abstract: Benzene is not formed in flames by high-pressure-limit addition reactions, as had been implied previously, but by chemically activated addition and isomerization reactions. First, mole-fraction and rate data for molecules and free radicals were measured in a lightly sooting, laminar, premixed flame of C{sub 2}H{sub 2}/O{sub 2}/Ar at 1000-1700 K and 2.67 kPa (20 Torr) by using molecular-beam mass spectrometry. Second, mechanisms were screened in this flame and a similar 1,3-butadiene flame by using high-pressure-limit rate constants. Third, pressure-dependent rate constants for all channels of successful mechanisms were analyzed by bimolecular quantum-RRK calculations. Finally, data tests with these more accurate rate constants showed that only additions of vinylic 1-C{sub 4}H{sub 5} and 1-C{sub 4}H{sub 3} radicals to C{sub 2}H{sub 2} were fast enough to account for the highest observed rates of benzene formation, forming benzene and phenyl directly by chemically activated channels. These reactants have been suggested before, but the pathways are crucially different from high-pressure-limit routes.