Quantum effects in the kinetics of the reaction O-2 + e -> O-2(-) have been evaluated theoretically. The spectral properties and the potential energy curves of the oxygen molecule and the superoxide ion were obtained from quantum DFT calculations at the G96PW91/6-311+G* level. From these curves, the vibrational eigenfunctions and eigenvalues of the reactant and the product were calculated. The corresponding non-adiabatic reduction rate was obtained from first-order perturbation theory. The partial contributions coming from the ground and excited states of both species are analyzed in detail. It is shown that the contribution of the O-2(-) excited states to the rate is negligibly small for low overpotentials. Their participation rises when higher overpotentials are applied. (c) 2005 Elsevier B.V. All rights reserved.