Geometry and Electronic Structure of the Hydroperoxyl Radical

Abstract

Ab initio self-consistent-field (SCF) and configuration-interaction (CI) calculations have been carried out to investigate the geometry and electronic structure of the 2A'' ground state of the HO2 radical. A slightly better than double-ζ basis set of contracted Gaussian functions was used. First-order wave functions including 500 configurations were used to describe electron correlation in HO2. The iterative natural orbital procedure was used to generate an optimum set of molecular orbitals. The SCF predicted geometry is r(H-O) = 0.968 Å, r(O-O) = 1.384 Å, and bond angle 106.8°. The first-order geometry is r(O-H) = 0.973 Å, r(O-O) = 1.458 Å, and bond angle 104.6°. Our bond angle is consistent with Walsh's prediction, and the overall geometry is in essential accord with that suggested by Paukert and Johnston. However, several earlier theoretical predictions are not consistent with our results. Force constants are predicted which suggest that the O-H bond is similar to that in water, but the O-O bond is much weaker than that in the O2 molecule. The H-O2 dissociation energy is predicted to 2.36 eV in the SCF approximation and 2.82 eV from CI, compared to an experimental value of 2 eV. The electronic structure of HO2 is discussed in terms of the natural orbital occupation numbers and the most important configurations. © 1971, American Chemical Society. All rights reserved.