title: Time- and Isomer-Resolved Measurements of Sequential Addition of Acetylene to the Propargyl Radical.
abstract: Soot formation in combustion is a complex process in which polycyclic aromatic hydrocarbons (PAHs) are believed to play a critical role. Recent works concluded that three consecutive additions of acetylene (C2H2) to propargyl (C3H3) create a facile route to the PAH indene (C9H8). However, the isomeric forms of C5H5 and C7H7 intermediates in this reaction sequence are not known. We directly investigate these intermediates using time- and isomer-resolved experiments. Both the resonance stabilized vinylpropargyl (vp-C5H5) and 2,4-cyclopentadienyl (c-C5H5) radical isomers of C5H5 are produced, with substantially different intensities at 800 K vs 1000 K. In agreement with literature master equation calculations, we find that c-C5H5 + C2H2 produces only the tropyl isomer of C7H7 (tp-C7H7) below 1000 K, and that tp-C7H7 + C2H2 terminates the reaction sequence yielding C9H8 (indene) + H. This work demonstrates a pathway for PAH formation that does not proceed through benzene.
authors.affiliation: Combustion Research Facility, Sandia National Laboratories , Mail Stop 9055, Livermore, California 94551-0969, United States.
authors.forename: John D
authors.initials: JD
authors.lastname: Savee
authors.affiliation: Combustion Research Facility, Sandia National Laboratories , Mail Stop 9055, Livermore, California 94551-0969, United States.
authors.forename: Talitha M
authors.initials: TM
authors.lastname: Selby
authors.affiliation: Combustion Research Facility, Sandia National Laboratories , Mail Stop 9055, Livermore, California 94551-0969, United States.
authors.forename: Oliver
authors.initials: O
authors.lastname: Welz
authors.affiliation: Combustion Research Facility, Sandia National Laboratories , Mail Stop 9055, Livermore, California 94551-0969, United States.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Taatjes
authors.affiliation: Combustion Research Facility, Sandia National Laboratories , Mail Stop 9055, Livermore, California 94551-0969, United States.
authors.forename: David L
authors.initials: DL
authors.lastname: Osborn
keywords: molecular weight growth; photoionization; resonance stabilized radicals; soot formation