Time- and Isomer-Resolved Measurements of Sequential Addition of Acetylene to the Propargyl Radical

• Published in: The journal of physical chemistry letters Vol. 6; no. 20; pp. 4153 - 4158
• Main Authors: Savee, John D, Selby, Talitha M, Welz, Oliver, Taatjes, Craig A, Osborn, David L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.10.2015
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; molecular weight growth; photoionization; resonance stabilized radicals; soot formation; resonance stabilized radicals; soot formation; molecular weight growth; photoionization
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.5b01896

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.