An ab initio investigation of possible intermediates in the reaction of the hydroxyl and hydroperoxyl radicals

Ab initio quantum chemical techniques are used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types are identified. Basis sets of polarized double zeta quality and large scale configuration interaction wave functions are utilized. Based on electronic energies, the covalently bonded HOOOH species is 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen bonded HO---HO2 species has an electronic energy 4.7 kcal/mol below that of the component radicals, after correction is made for the basis set superposition error. The hydrogen bonded form is planar, possesses one relatively normal hydrogen bond, and has the lowest energy 3A' and 1A' states that are essentially degenerate. The 1A" and 3A" excited states produced by rotation of the unpaired OH electron into the molecular plane are very slightly bound

Quantum chemical study of methane oxidation species

Work completed on the 2A1 excited state and low-lying dissociative states of the methoxy radical is reported. A manuscript was prepared that reports the characterization of the 2A1 electronic state, the excitation energies and Franck-Condon factors for the 2A1 - 2E system, and the energies of intersection between the 2A1 state and the nearby dissociative states. The minimum excitation energy needed for predissociation of methoxy is predicted along with the corresponding implications for atmospheric chemistry

The search for protonated dihydrogen trioxide (HOOOH) : insights from theory and experiment

Protonated dihydrogen trioxide (HOOOH) has been postulated in various forms for many years. Protonation can occur at either the terminal (HOOO(H)H+) or central (HOOH(OH)+) oxygen atom. However, to date there has been no definitive evidence provided for either of these species. In the current work we have employed ab initio methods, CCSD(T) and MP2, with a large basis set (6-311++G(3df,3pd)) to determine the relative stabilities of these species. It is shown that the terminally protonated species is strongly favored relative to the centrally protonated species (ΔE ) 15.8 kcal/mol, CCSD(T)//MP2). The mechanism of formation of HOOO(H)H+ was determined to occur with a low barrier with the H3O+ occurring in a thermoneutral reaction (ΔE)-0.3 kcal/mol, CCSD(T)//MP2). Although HOOO(H)H+ exists as a stable intermediate, it is extremely short-lived and rapidly decomposes (ΔE* ) 8.6 kcal/mol, MP2) to H3O+ and O2(1Δg). The decomposition reaction is stabilized by solvent water molecules. The short-lived nature of the intermediate implies that the intermediate species can not be observed in 17O NMR spectra, which has been demonstrated experimentally