Electron spin resonance spectrum of the O –2 radical ion trapped in non-ionic matrices at 77 °K

Abstract

Trapped electrons are formed when alkali metal atoms are deposited on water or alcohols at 77 °K in the rotating cryostat. However, when trace amounts of oxygen are also admitted during deposition the deep colour and characteristic electron spin resonance (e.s.r.) spectrum of the trapped electrons are absent. Instead, the deposit is white and gives a highly asymmetric e.s.r. spectrum which has basically the same form in all of the solvents. However, the principal value g∥ of the g-factor varies slightly, but significantly, with the solvent in which the radical ion is trapped. Identical spectra in the corresponding solvents are observed from (a) frozen samples of water or alcohols which have been saturated with oxygen and then irradiated at 77 °K with cobalt-60γ-rays; and also from (b) samples which have been prepared by rapidly stirring sodium superoxide NaO₂ into the solvent at room temperature and then immediately freezing the resultant slurry in liquid nitrogen (77°K).

All of the e.s.r. spectra observed in these three groups of experiments arise from the O^–₂ radical ion which is trapped by an assembly of solvent molecules similar to the postulated for electrons trapped in the same solvents. The variation of g∥ with the solvent in which the radical ion is trapped is similar to that found for the energy of the maximum absorption in the optical spectra of electrons trapped in these solvents and reflects the degree of interaction between the ion and the solvent.