Computational Study of the Reaction Mechanism of the Methylperoxy Self-Reaction

To provide insight on the reaction mechanism of the methyperoxy (CH₃O₂•) self-reaction, stationary points on both the spin-singlet and the spin-triplet potential energy surfaces of 2(CH₃O₂•) have been searched at the B3LYP/6-311++G(2df,2p) level. The relative energies, enthalpies, and free energies of these stationary points are calculated using CCSD(T)/cc-pVTZ. Our theoretical results indicate that reactions on a spin-triplet potential energy surface are kinetically unfavorable due to high free energy barriers, while they are more complicated on the spin-singlet surface. CH₃OOCH₃ + O₂¹ can be produced directly from 2(CH₃O₂•), while in other channels, three spin-singlet chain-structure intermediates are first formed and subsequently dissociated to produce different products. Besides the dominant channels producing 2CH₃O• + O₂ and CH₃OH + CH₂O + O₂ as determined before, the channels leading to CH₃OOOH + CH₂O and CH₃O• + CH₂O + HO₂• are also energetically favorable in the self-reaction of CH₃O₂• especially at low temperature according to our results.