Rate rules for hydrogen abstraction reaction kinetics of polycyclic aromatic hydrocarbons and vinyl radical

Abstract

Hydrogen abstraction reaction from polycyclic aromatic hydrocarbons (PAHs) is an important reaction class for PAHs consumption and soot formation. In this work, the reaction kinetics for a series of PAHs containing up to seven aromatic rings by vinyl radical are systematically investigated using the M06-2X/cc-pVTZ method. Based on the electronic structure calculations, the rate constants of title reactions are calculated by using transition state theory coupled with Eckart tunneling correction at the temperature range of 500–2500 K. The effects of PAH sizes, structures, and reaction sites on the rate constants are examined. The results show that the PAH sizes and reaction sites have little effect on the rate constants, while the structures of PAHs influence the rate constant significantly. Hence, the hydrogen abstraction reactions are simplified into C5 and C6 reaction classes depending on the abstraction site on the five- or six-membered ring. The simple two classes are conducive to construct the combustion model of PAHs. The reactivity with C6 class possesses the higher activity than the C5 class. Moreover, the difference in rate constants between the two classes is large at low temperatures while the two reaction classes are competitive above 1000 K. The rate rules are summarized by taking the average values of rate constants of a representative set of reactions in each class, which are applicable for the chemical model construction of PAHs.