title: Role of phenyl radicals in the growth of polycyclic aromatic hydrocarbons.
abstract: To investigate the role of phenyl radical in the growth of PAHs (polycyclic aromatic hydrocarbons), pyrolysis of toluene with and without benzene has been studied by using a heatable tubular reactor couple with an in-situ sampling vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometer (TOFMS) at temperatures 1155-1467 K and a pressure of 10.02 Torr with 0.56 s residence time. When benzene was added, a significant increase of phenyl addition products (biphenyl, terphenyl, and triphenylene) was observed and the mass spectra showed a clear regular sequence with an interval of approximately 74 mass number, corresponding to the phenyl addition (+C6H5) followed by H-elimination (-H) and cyclization (-H2). The analysis showed that the PAC (phenyl addition/cylization) mechanism is efficient for the growth of PAHs without a triple fusing site, for which the HACA (hydrogen abstraction/C2H2 addition) step is inefficient, and produces PAHs with five-membered rings. The PAC process was also suggested to be efficient in the subsequent growth of PAHs with five-membered rings. The role of the PAC mechanism in combustion conditions is discussed in relation to the importance of disordered five-membered ring structure in fullerene or soot core.
authors.affiliation: Department of Chemical System Engineering, The University of Tokyo, 7-3-1, Bunkyo-ku, Hongo, Tokyo, 113-8656, Japan.
authors.forename: Bikau
authors.initials: B
authors.lastname: Shukla
authors.forename: Akio
authors.initials: A
authors.lastname: Susa
authors.forename: Akira
authors.initials: A
authors.lastname: Miyoshi
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Koshi