Theoretical study of important phenylacetylene reactions in polycyclic aromatic hydrocarbon growth

Phenylacetylene is of significance in polycyclic aromatic hydrocarbon (PAH) growth in combustion systems, especially as the key intermediate species in the hydrogen abstraction carbon addition sequence. The consumption of phenylacetylene via H-atom abstraction reactions forming ortho-C₆H₄C₂H (o-C₆H₄C₂H) radical and its subsequent reaction with carbon addition are important steps in PAH growth. Nevertheless, rate constants for H-atom abstraction reactions from phenylacetylene have not been explored theoretically in the literature. As regards carbon addition, besides acetylene, ethylene is also presented in large concentrations in e.g., ethylene and propene flames. However, its role in PAH growth has not been well addressed yet. In this study, the H-atom abstraction reactions from phenylacetylene aromatic ring sites (ortho-, meta-, para-) by both H atoms and OH radicals, and the subsequent C₂H₄ addition to o-C₆H₄C₂H radical are accurately determined with electronic structure calculations. The main bimolecular product from the potential energy surface of the C₂H₄ addition to o-C₆H₄C₂H is 2-ethynylstyrene + H, while naphthalene + H and 1-methyleneindene + H are preferred to form at high temperatures and low pressures. Rate constants are lumped with an automated master equation-based lumping approach and integrated into a recently developed chemical kinetic model. Updates of the phenylacetylene-related reactions are tested by ethylene and benzene copyrolysis in shock tube, and ethylene oxidation in laminar premixed and counterflow diffusion flames. Reaction flux analysis are additionally performed regarding the phenylacetylene consumption and naphthalene formation.