A thorough theoretical mechanistic study of OH-initiated oxidative degradation mechanism for large polycyclic aromatic hydrocarbons

Abstract

To get a better understanding of oxidative degradation of polycyclic aromatic hydrocarbons (PAH) in the atmospheric and combustion chemistry, benzo[ghi]perylene (BP) was selected as their prototype to be investigated by combining ab initio electronic structure theory calculations (M06-2X/6-31G(d,p)) and the conventional transition state theory. For BP-OH adducts, O2 addition favored the armchair edge comparing with the free and zigzag ones. The overall rate constant was increased due to the presence of armchair site; and thereby it has a prompt effect on the oxidation reactivity. This implies that given an arbitrary shaped PAH, OH attack preferentially occurs at the free-edge sites and subsequent O2 attack favors the armchair-edge sites. Morever, the current study provides new kinetics and thermodynamics data for OH-initiated oxidative degradation mechanism of benzo[ghi]perylene in a wider temperature range, which can be used for modeling the fate of large PAHs during combustion and in the atmosphere.