A review of literature data on relative abundances of various polycyclic aromatic hydrocarbons (PAH) in combustion flames and environmental samples shows that certain PAH molecules, including phenanthrene and acenaphthalene, pyrene and fluoranthene, and benzo(a)pyrene (one of the most carcinogenic PAH), are present in larger concentrations than other PAHs with the same number of aromatic rings. In our study, we attempt to link relative abundances of different PAH isomers to their formation mechanisms from naphthalene through hydrogen-abstraction-C2H2-addition (HACA) routes. In particular, we investigate potential energy surfaces relevant to the formation of anthracene, phenathrene, and acenaphthalene from naphthalene via the HACA mechanism using high-level ab initio G3-type calculations and then employ rate constant calculations to evaluate relative yields of these molecules at different temperatures. The results indicate that the pathways from 1-naphthyl dominantly form acenaphthalene and those from 2-naphthyl give phenanthrene and anthracene with the former being produced at a higher yield.

HACA mechanism revised: Formation of PAHs beyond the second aromatic ring

245th National Meeting (2013)

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