Effect of solvation on the electron spin resonance spectrum of the superoxide ion

Abstract

The solvation of superoxide ions by protic solvents has been studied by e.s.r. spectroscopy. It is concluded that strong hydrogen bonds lift the degeneracy of the π-orbitals, with solvation being effectively confined to one of these orbitals. It is suggested that, when aqueous solutions are frozen, phase separation occurs so that the g_z value (2.11) is not characteristic of the aquated ion. By extrapolation from data for aqueous methanolic glasses, we obtain a g_z value of 2.065 for the aquated ion.

Solutions in dry aprotic solvents generally give broad g_z features at much lower fields. However, water in low concentrations is scavenged by the anions and this results in a shift of the g_z feature into the 2.1 region. It is suggested that dry O^–₂ may add reversibly to dimethyl formamide to give a peroxy-radical adduct. Ion-pair formation with divalent cations has also been studied.