Quantum chemical and RRKM investigation of the elementary channels of the reaction C6H6+O(P-3)

We performed a computational study of an important reaction in the combusti on of hydrocarbons, C6H6, + O (P-3), using ab initio and RRKM methods. Dens ity functional theory (B3LYP) was used to optimize geometries and obtain mo lecular vibrational frequencies. and complete basis set extrapolation (CBS- QB3) was used to obtain the energies for the reactants several transition s tates and products. The initial formation of a stabilized adduct is charact erized by a barrier of 4.9 kcal mol(-1), in good agreement with the measure d activation energy for this reaction. All product channels originate from rearrangement or decomposition of this adduct, which our calculations sugge st is a triplet ground state, All of our ab initio calculations are thus co nducted on the triplet surface. There are several products that are energet ically accessible at combustion temperatures, but the formation of phenoxy radical, C6H5O, and H atom dominate the product slate at low temperatures. Rearrangement to form formylcyclopentadiene, C5H5CHO, is also important at low temperatures, and the decomposition of this species to form cyclopentad ienyl radical, C5H5, and HCO may be significant at higher temperatures. Rea rrangement to form phenol is unimportant at all temperatures.