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Ethylene combustion products obtained over a range of conditions regularly show peaks with retention times and mass spectra expected for C 20 H 10 polycyclic aromatic hydrocarbons (PAH) when analyzed by gas chromatography/mass spectrometry (GC/MS). Analysis by high-performance liquid chromatography with spectrometric diode-array detection (HPLC/DAD) yields three distinct peaks over the C 20 PAH elution interval whose UV-vis spectra differ from those of known PAH. These results, highly characteristic of ethylene flames, strongly suggested the presence of at least three C 20 H 10 PAH. Recent progress in PAH synthesis permitted the comparison of chromatographic and spectrometric data for flame samples with those of authentic dicyclopentapyrenes: dicyclopenta[cd,fg]pyrene, dicyclopenta[cd,mn]pyrene, and dicyclopenta [cd,jk]pyrene. The comparative analysis established that the three C 20 H 10 PAH long observed in ethylene flames were indeed the three dicyclopentapyrene isomers. Additional analysis of samples from a range of flames showed that the dicyclopentapyrenes are present in fullerene-deficient flames, but are absent in fullerene-producing flames. The dicyclopentapyrenes are notable for being isomers of corannulene, a possible fullerene precursor also found in a range of flames. The significance of these findings in relation to the flame production of fullerenes is discussed.

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Oxidation and hydrolysis reactions of benzene in supercritical water were in®estigated thoroughly using experimental measurements. Little to no reaction occurred without oxygen at temperatures between 530 and 625ЊC for residence times up to 6 s. Oxidation reactions were studied at temperatures ranging from 479 to 587ЊC, pressures of 139 to 278 bar, reactor residence times from 3 to 7 s, and with ®arying initial benzene concentrations from 0.4 to 1.2 mmolrL and oxygen concentrations from 40% of oxygen demand to 100% excess oxygen. To a 95% le®el of statistical confidence, the oxidation rate was found to be of 0.04 " 0.07 order in benzene, 0.17 " 0.05 order in oxygen, and 1.4 " 0.1 order in water, with an acti®ation energy of 270 " 10 kJrmol. The primary oxidation product at all reaction conditions studied was carbon dioxide. Other important oxidation products were carbon monoxide, phenol, and methane. Trace le®els of additional light hydrocarbon gases and single-and multi-ringed aromatic species were also detected under some conditions.