Ab initio study of the CH 3 O 2 self‐reaction in gas phase: Elucidation of the CH 3 O 2 CH 3 O 2 → 2CH 3 O O 2 pathway

Ab initio electronic structure calculations have been performed to determine the mechanism governing the 2CH 3 O 2 → 2CH 3 O + O 2 chemical reaction in gas phase. Geometry optimizations for reactants, intermediates, transition states, and products were performed at the MP2 level of theory with the 6‐311G(2 d ,2 p ) basis sets. Further, PMP4(SDTQ)/6‐311G(3 df ,2 p ) single‐point calculations were performed on the previous MP2/6‐311G(2 d ,2 p )‐optimized geometries. For the past 50 years, it has been proposed that the production of CH 3 O and O 2 in the self‐reaction of methylperoxyl radicals is the result of the direct dissociation of a noncyclic tetraoxide intermediate via a concerted mechanism involving a single step. Our theoretical results indicate that the reaction path is more complex than expected. We found that the reaction proceeds through a nonconcerted mechanism involving two tetraoxide intermediates that have different geometries and relative energies. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004