Theoretical study on the HACA chemistry of naphthalenyl radicals and acetylene: The formation of C12H8, C14H8, and C14H10 species

The hydrogen-abstraction-C2H2-addition (HACA) chemistry of naphthalenyl radicals has been studied extensively, but there is a significant discrepancy in product distributions reported or predicted in literature regarding appearance of C(14)H(8)and C(14)H(10)species. Starting from ab initio calculations, a comprehensive theoretical model describing the HACA chemistry of both 1- and 2-naphthalenyl radicals is generated. Pressure-dependent kinetics are considered in the C12H9, C14H9, and C(14)H(11)potential energy surfaces including formally direct well-skipping pathways. On the C12H9PES, reaction pathways were found connecting two entry points: 1-naphthalenyl (1-C10H7) + acetylene (C2H2) and 2-C10H7+ C2H2. A significant amount of acenaphthylene is predicted to be formed from 2-C10H7+ C2H2, and the appearance of C(14)H(8)isomers is predicted in the model simulation, consistent with high-temperature experimental results from Parker et al. At 1500 K, 1-C10H7+ C(2)H(2)mostly generates acenaphthylene through a formally direct pathway, which predicted selectivity of 66% at 30 Torr and 56% at 300 Torr. The reaction of 2-C(10)H(7)with C(2)H(2)at 1500 K yields 2-ethynylnaphthalene as the most dominant product, followed by acenaphthylene mainly generated via isomerization of 2-C(10)H(7)to 1-C10H7. Both the 1-C(10)H(7)and 2-C(10)H(7)reactions with C(2)H(2)form some C(14)H(8)products, but negligible phenanthrene and anthracene formation is predicted at 1500 K. A rate-of-production analysis reveals that C(14)H(8)formation is strongly affected by the rates of H-abstraction from acenaphthylene, 1-ethynylnaphthalene, and 2-ethynylnaphthalene, so the kinetics of these reactions are accurately calculated at the high level G3(MP2,CC)//B3LYP/6-311G*level of theory. At intermediate temperatures like 800 K, acenaphthylene + H are the leading bimolecular products of 1-C10H7+ C2H2, and 1-acenaphthenyl radical is the most abundant C(12)H(9)isomer due to its stability. The predicted product distribution of 2-C10H7+ C(2)H(2)at 800 K, in contrast to the results of Parker et al is predicted to consist primarily of species containing three fused benzene rings-for example, phenanthrene and anthracene-as the leading products, indicating HACA chemistry is valid from two to three ring polycyclic aromatic hydrocarbons under some conditions. Further experiments are needed for validation.