Mechanism of the Participation of Water in the Decomposition of Hydrogen Trioxide (HOOOH). A Theoretical Study

Ab initio calculations at the MP4//MP2/6-31++G* level of theory have shown a substantial reduction (by 33.5 kcal/mol) of the energy barrier for the intramolecular 1,3-proton transfer in HOOOH to give water and singlet oxygen (Δ¹O₂), when a molecule of water, acting as a bifunctional catalyst, was allowed to participate in the process. The energy barriers, ΔE^⧧ = 15.1 and 26.0 kcal/mol, relative to isolated reactants and HOOOH−HOH complex, respectively, were calculated. The following gas-phase acidity order was found:  HOOOH (352 kcal/mol) > HOOH (376 kcal/mol) > HOH (391 kcal/mol). HOOO^- was calculated to possess an exceptionally long HO−OO^- bond (1.96 Å), indicating dissociation into HO^- and O₂. It is most likely that this species does not exist as a distinguished molecular entity in water solutions of HOOOH.