Public reporting burden for this collection of information is estimated to average 1 hour per response, including the tane for reviewing instnictons. searching existing data sources, gathering and maintaining the data needed, and comnpleting and reviewing this coltlction of information. SPONSORING I MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR/MONITOR'S ACRONYM(S)AFOSR SUPPLEMENTARY NOTES ABSTRACTSupercritical pyrolysis experiments were conducted with three model fuels at temperatures up to 585 °C and pressures up to 110 atm. The products were analyzed by gas chromatography and high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance and mass spectrometric detection, a technique ideally suited for the isomer-specific analysis of polycyclic aromatic hydrocarbons (PAH), which can serve as precursors to carbonaceous solids. Thirty-nine individual 2-to 9-ring PAH were identified in the supercritical 1-methylnaphthalene pyrolysis products-seventeen of which, for the first time.Reaction pathways involving l-naphthylmethyl, methyl, and naphthyl radicals were developed to account for the formation of the observed PAH products and explain why unobserved PAH were not formed in the supercritical I -methylnaphthalene pyrolysis environment. Likewise, reaction pathways involving benzyl, methyl, and phenyl radicals were developed that accounted for the formation of the forty-four individual PAH identified as supercritical toluene pyrolysis products and explained why unobserved PAH were not formed. The PAH product distribution from methylcyclohexane was extremely similar to that of toluene, indicating that the PAH formation mechanisms devised for toluene applied to supercritical methylcyclohexane as well.