Theoretical Study of the HOCH2OO center dot + HO2 center dot Reaction: Detailed Molecular Mechanisms of the Three Reaction Channels

The HO2 + HOCH2OO reaction was theoretically investigated using various high level single reference Complete Basis Set methods including CBS QB3 CBS QCI/APNO and CBS Q(MPW1B95) and a new multi reference CI PT2 approach Three major product channels under atmospheric conditions were identified and their molecular mechanisms elucidated in great detail by Intrinsic Reaction Coordinate Analyses (IRC) at the B3LYP/6-311G(d p) level (i) Direct head to tail H atom abstraction from the hydroperoxy radical by the alkylperoxy occurring on the triplet Potential Energy Surface (PES) leading to HOCH2OOH + O-2 (ii) A two step rearrangement of the initial singlet HOCH2OOOOH tetroxide complex to form HC(O)OH + OH + HO2 (iii) A multi step rearrangement of the initial HOCH2OOOOH tetroxide to yield HC(O)OH + O-2((1 Delta)A) + H2O about twice as fast as the former channel on the singlet surface The findings provide an explanation for the observed hydroxyl radical formation in this reaction (Jenkin et al Phys Chem Chem Phys 9 (2007) 3149) and rationalize the high overall rate and its pronounced negative temperature dependence (Veyret et al J Phys Chem 93 (1989) 2368)