An a b i n i t i o investigation of possible intermediates in the reaction of the hydroxyl and hydroperoxyl radicals

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Abstract
A b initio quantum chemical techniques have been 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 were identified. Basis sets of polarized double-zeta quality and large scale configuration interaction wave functions have been utilized. Based upon electronic energies, the covalently-bonded HOOOH species is found to be 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen-bonded HO---HO2 species is found to have 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 found to be planar, to possess one relatively ‘‘normal’’ hydrogen bond, and to have 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 found to be very slightly bound.