The unimolecular decomposition of bicyclic alkoxy radicals and their subsequent ring-cleavage acyclic radicals from the OH-initiated reactions of toluene is investigated by means of theoretical quantum chemistry methods. The reaction and activation energies of ring-cleavage of the bicyclic alkoxy radicals are in the ranges of -45.9 to -54.5 kcal mol(-1) and 5.5-11.3 kcal mol(-1), respectively. The activation energies of C-C bond cleavage of the acyclic radicals are in the range of 2.5-27.0 kcal mol(-1). Kinetic calculations employing RRKM/ME formalism have been performed to assess the fate of chemically excited acyclic radicals for prompt decomposition or stabilization. The results indicate that the favorable decomposition pathways of the bicyclic alkoxy radicals correspond to the formation of dicarbonyl compounds along with glyoxal and methylglyoxal. (c) 2006 Elsevier B.V. All rights reserved.