Computational study of polycyclic aromatic hydrocarbons growth by vinylacetylene addition

Abstract

The growth of polycyclic aromatic hydrocarbons (PAH) can proceed via multiple chemical mechanisms. The mechanism of naphthyl radical and vinylacetylene (C4H4) addition reaction has been systematically investigated in this computational study. A combination of DFT/B3LYP/6-311+G(d,p), CCSD/6-311+G(d,p) and CBS-QB3 methods were performed to calculate the potential energy surfaces. It revealed that the products, including phenanthrene, anthracene, a PAH with a five-membered ring structure, and PAH with a C4H3 radical substitution, can be formed in A2-1 (1-naphthyl)+C4H4 and A2-2 (2-naphthyl) +C4H4 reaction networks. The reaction rate constants at 0.1-100 atm were evaluated by RRKM theory by solving the master equation in the temperature range of 800-2500 K, which showed that the rate constants of reactions A2-1 (A2-2)+C4H4→product+H are highly temperature-dependent but nearly pressure-independent. The distribution of products was investigated in a 0-D batch reactor, wherein the initial reactant concentrations were taken from experimental measurements. The results showed that adduct intermediates were the main products at low temperature (T < 1000 K), and the phenanthrene and PAH with C4H3 radical substitution became the dominant products at temperatures where PAHs and soot form in flames (T > 1000 K). It was observed that a significant amount of phenanthrene is formed from PAH with a C4H3 radical substitution with the assistance of H atom. Reaction pathway sensitivity analysis for the PAH radical+C4H4 reaction system was performed and showed that the new benzene rings are more likely to be generated near the zigzag edge surface site instead of the free edge. For the development of a PAH mechanism, the analogous treatment of rate constants for larger PAH radical + C4H4 reaction system are discussed. The formation rate of naphthalene from the reaction of phenyl+C4H4 was found to be very close to that of phenanthrene from the reaction of naphthyl+C4H4, suggesting that the analogous treatment of the rates is reasonable in PAH mechanisms.

Formation of Phenanthrene via Recombination of Indenyl and Cyclopentadienyl Radicals: A Theoretical Study

“…Because of their importance, the mechanistic studies on the PAH formation and growth have taken the central stage in modern combustion research. A variety of molecular growth mechanisms have been proposed for PAH including HACA − (hydrogen abstraction–acetylene addition or, more generally, H-activated carbon addition), HAVA − (hydrogen abstraction–vinylacetylene addition), PAC − (phenyl addition/dehydrocyclization), and others . These mechanisms normally involve repetitive sequences of two principal steps: H atom abstraction activating an aromatic molecule followed by the addition of a closed-shell hydrocarbon to the aromatic radical resulting in the formation of (an) extra ring(s) via cyclization and aromatization.…”

Furan formation pathways exploration in low temperature oxidation of 1,3-butadiene, trans-2-butene, and cis-2-butene

“…For example, one furan formation pathway starting from 1,3-butadiene mainly consists of 1,3-butadiene + OH → 2,5-dihydrofuran (P1-8) + H, 1,3-butadiene + HO2 → 2,5-dihydrofuran + OH, and P1-8 + H → S1-14 + H2. The pressure-dependence of reaction rate coefficients in these bimolecular reactions is expected to be ignorable according to previous studies [37]. Moreover, the pressure-dependence of rate coefficients of decomposition reactions becomes weak in the investigated temperature range of 500-900 K, as evidenced by [38,39].…”

Clar Covers of Overlapping Benzenoids: Case of Two Identically-Oriented Parallelograms

“…Benzenoid hydrocarbons are an intensively studied class of aromatic molecules attracting attention of scientists specializing in various fields of chemistry including organic synthesis [1,2] and characterization [3][4][5], combustion chemistry [6,7], nanoscience [8,9], atmospheric chemistry [10,11], astrochemistry [12,13], computational chemistry [14,15], and chemical graph theory [16,17]. Enumeration and construction of Clar covers for benzenoid hydrocarbons constitutes one of the important branches of chemical graph theory.…”

“…is the 2D dihedral group) and selecting a structure for which µ ≥ ν and m 1 ≥ m 2 . Perhaps such a solution is aesthetically pleasing, but from a practical standpoint it is more convenient to use a symmetry-adapted version of Equations (15) and (19) given by the following expression…”