Hydrogen Abstraction Acetylene Addition and Diels−Alder Mechanisms of PAH Formation:  A Detailed Study Using First Principles Calculations

Abstract

Extensive ab initio Gaussian-3-type calculations of potential energy surfaces (PES), which are expected to be accurate within 1-2 kcal/mol, combined with statistical theory calculations of reaction rate constants have been applied to study various possible pathways in the hydrogen abstraction acetylene addition (HACA) mechanism of naphthalene and acenaphthalene formation as well as Diels-Alder pathways to acenaphthalene, phenanthrene, and pyrene. The barrier heights; reaction energies; and molecular parameters of the reactants, products, intermediates, and transition states have been generated for all types of reactions involved in the HACA and Diels-Alder mechanisms, including H abstraction from various aromatic intermediates, acetylene addition to radical sites, ring closures leading to the formation of additional aromatic rings, elimination of hydrogen atoms, H disproportionation, C2H2 cycloaddition, and H2 loss. The reactions participating in various HACA sequences (e.g., Frenklach's, alternative Frenklach's, and Bittner and Howard's routes) are demonstrated to have relatively low barriers and high rate constants under combustion conditions. A comparison of the significance of different HACA mechanisms in PAH growth can be made in the future using PES and molecular parameters obtained in the present work. The results show that the Diels-Alder mechanism cannot compete with the HACA pathways even at high combustion temperatures, because of high barriers and consequently low reaction rate constants. The calculated energetic parameters and rate constants have been compared with experimental and theoretical data available in the literature.

Role of Hydrogen Abstraction Acetylene Addition Mechanisms in the Formation of Chlorinated Naphthalenes. 1. A Quantum Chemical Investigation

“…58 These values compare reasonably well with the α-chlorinated addition of C 2 HCl to I3 and I7 via TS30 and TS32, respectively. β-Chlorinated addition steps, via TS29 and TS31, overcome barriers ∼15 kJ mol −1 lower than those through TS30 and TS32, respectively.…”

Kinetic modeling study of benzene and PAH formation in laminar methane flames

“…This model adopts an estimated rate of this reaction by Matsugi and Miyoshi [54] and Zhang et al [66] in their modeling studies on the pyrolysis of toluene. Meanwhile, Matsugi and Miyoshi [54] also estimated the rate constant of the recombination of benzyl (A 1 CH 2 ) and acetylene (R52) based on the calculation of Kislov et al [115] and Vereecken et al [116,117] between 1000 and 4000 K. Another rate constant was provided by Vereecken et al [116,117] within the temperature range of 200-2000 K. The estimation by Blanquart et al [69] was used in this model, which agreed well with the latter value.…”

A consistent chemical mechanism for oxidation of substituted aromatic species

“…Both rate constants were taken from Kislov and Mebel [44]. Phenylacetylene may also be formed by various H-abstraction reactions from A 1 C 2 H 2 .…”