Identification of some novel cyclopenta-fused polycyclic aromatic hydrocarbons in ethylene flames

The product suite of polycyclic aromatic hydrocarbons (PAH) produced in typical high-temperature (1300-1700 K) 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]fluor anthene. 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 C-5-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 C(24)H(12)PAH (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. Identification of the three new PAH was accomplished by comparing spectral and chromatographic signatures with those of the references standards using gas chromatography/mass spectrometry and high performance liquid chromatography with spectrometric diode-array detection. Selected spectral data are presented for the three new species.