The potential energy surface (PES) of the C6H5. + O-2((3)Sigma(g)) reaction has been studied using the B3LYP method. Several pathways were considered following the formation of the phenylperoxy (C6H5OO.) radical. At low temperatures (T < 432 K), the lowest energy pathway was found to go through a dioxiranyl radical. Scission of the O-O bond to form the phenoxy (C6H5O.) radical and O(P-3) atom is more favorable at higher temperatures. Transition state structures for several steps in the decomposition of the phenylperoxy radical are presented to augment the C6H5. + O-2 PES. For the heteroatomic aromatic hydrocarbon radicals, such as pyridine, furan, and thiophene, only minima on the PES are calculated in analogy with the intermediates obtained for the reaction of phenyl radical with O-2. One important result of the proposed decomposition mechanism is that subsequent rearrangements of the heteroatomic aromatic hydrocarbon peroxy radicals (Ar-OO.) are likely to yield intermediates that are of atmospheric interest.