The identification of cyclopenta-fused and ethynyl-substituted polycyclic aromatic hydrocarbons in benzene droplet combustion products

In order to investigate new aspects of polycyclic aromatic hydrocarbon (PAH ) growth and soot formation, we have synthesized special reference standard s of cyclopenta-fused PAH (CP-PAH) and ethynyl-substituted PAH. We have ide ntified several of these CP-PAH and ethynyl-PAH in benzene droplet combusti on products, using high pressure liquid chromatography (HPLC) and ultraviol et-visible (UV) absorption spectroscopy. Although one CP-PAH identified in these products-acenaphthylene has previously been identified as a product o f a variety of combustion systems, we have identified six additional CP-PAH and two ethynyl-PAH which have never before been unequivocally identified as the products of benzene pyrolysis or combustion: acephenanthrylene, ace- anthrylene, cyclopent[hi]acephenanthrylene, cyclopenta[cd]fluoranthene, cyc lopenta[cd] pyrene, dicyclopenta[cd,jk]pyrene, 2-ethynylnaphthalene, and 1- ethynylacenaphthylene. We present the corresponding UV absorption spectra o btained from the HPLC analysis of benzene droplet combustion products, and compare them to the UV absorption spectra we have obtained from specially s ynthesized reference standards. We also present the UV absorption spectra o f two additional ethynyl-PAH reference standards-3-ethynylfluoranthene and 1-ethynylpyrene-which we have synthesized.