(644e) New Insights Into the Ozonolysis of Surface-Adsorbed Polycyclic Aromatic Hydrocarbons

The environmental fate of polycyclic aromatic hydrocarbons (PAHs), from small species consisting of a few fused aromatic rings to man-made graphene-based nanomaterials, is an issue of pressing importance in ecology and public health. We have used a combination of laboratory experiments and ab initio simulations to gain insight into the mechanisms of ozone oxidation of surface-bound molecules in the PAH family, including anthracene, benzo[a]pyrene (BaP), and graphene sheets. We performed geometry optimizations and vibrational frequency calculations using density functional theory (B3LYP/6-31g**) for anthracene/O3 and BaP/O3 oxidation products and intermediates that have been suggested in the literature. We have identified oxidation pathways that require significant distortion of the PAH molecule from the native planar geometry in order to be energetically favorable, and others that do not. A pathway requiring distortion may be unfavorable for species interacting strongly with a rigid substrate. Our results provide new insight into the role of substrate in PAH oxidation. We will discuss these results in the context of the experimental data from our laboratory and in the literature.