Characterization of the potential energy surface of the HO2 molecular system by a density functional approach

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Abstract
The potential energy surface for the ground electronic state of the HO2 system has been characterized using extended basis sets with a recently introduced density functional incorporating gradient corrections and some Hartree–Fock exchange. All the structural, thermodynamic and spectroscopic properties of the hydroperoxide radical and of its molecular fragments (OH, O2) are in close agreement with experiment. The saddle points for HO2 isomerization and OO–H dissociation, together with the hydrogen bonded OH–O structure, have been fully characterized. Refined post Hartree–Fock computations have been performed to further validate density functional results. The two series of quantum mechanical computations are in good agreement and suggest some refinement of the most recent semiempirical surfaces developed for dynamical studies. This task can be made easier by the force fields of all the stationary points computed in the present work. These findings together with the very favorable scaling of the computations with the number of electrons suggest that the density functional approach is a promising theoretical tool for the study of reactions involving large, chemically significant species.