| Abstract
| - We report an investigation of the mechanistic features of OH-initiated oxidation reactions of p-xylene usingdensity function theory (DFT). Reaction energies for the formation of the aromatic intermediate radicalshave been obtained to determine their relative stability and reversibility, and their activation barriers havebeen analyzed to assess the energetically favorable pathways to propagate the p-xylene oxidation. OH additionis predicted to occur dominantly at the ortho position, with branching ratios of 0.8 and 0.2 for ortho and ipsoadditions, respectively, and the calculated overall rate constant is in agreement with available experimentalstudies. Under atmospheric conditions, the p-xylene peroxy radicals arising from initial OH and subsequentO2 additions to the ring are shown to cyclize to form bicyclic radicals, rather than to react with NO to leadto ozone formation. With relatively low barriers, isomerization of the p-xylene bicyclic radicals to morestable epoxide radicals likely occurs, competing with O2 addition to form bicyclic peroxy radicals. The studyprovides thermochemical and kinetic data for assessment of the photochemical production potential of ozoneand formation of toxic products and secondary organic aerosol from p-xylene oxidation.
|
