Identification of Some Novel Cyclopenta-Fused Polycyclic Aromatic Hydrocarbons in Ethylene Flames

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Abstract
The product suite of polycyclic aromatic hydrocarbons (PAH) produced in typical hightemperature (1300–1700K) fuel-rich flames is characterized by the abundance of peripherally-fused cyclopenta-PAH (CP-PAH), the most prominent of which are acenaphthylene (C12H8) and cyclopenta[cd]pyrene (C18H10). Although many other CP-PAH are thought to be present, their structural elucidation has been contingent on the availability of synthetic reference standards, and this has hindered their positive identification in flames. Previous studies using synthetic standards have resulted in the identification of a limited number of other CP-PAH including cyclopent[hi]acephenanthrylene, cyclopent[hi]aceanthrylene and all three isomeric dicyclopentapyrenes. In this work, we report the identification in ethylene flames of three additional CP-PAH, benzo[ghi]cyclopenta[cd]perylene, cyclopenta[bc]coronene and cyclopenta[cd]fluoranthene. Their positive identification was made possible by the availability of reference quantities of the authentic standards. Cyclopenta[bc]coronene is a C26H12 PAH (324 u) formed by the peripheral fusion of a C5-ring to coronene. It is one of the five most abundant PAH in ethylene flames typically accounting for 4%–6% of the total PAH for a range of flame types and operating conditions. Benzo[ghi]cyclopenta[cd]perylene is a C24H12PAH (300 u) isomeric with coronene. Cyclopenta[cd]fluoranthene is a C18H10 PAH presesent at low levels in the flames studied. It is much less abundant than its isomeric counterpart, cyclopenta[cd]pyrene, the most abundant PAH in ethylene flames.

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