Electron Spin Resonance Studies of the Formation of Anion Radicals on γ-Irradiated Silica Gel

The ESR spectra assigned to the anion radicals of SO2−, (TCNE)− (tetracyanoethylene), and O2− were obtained for, respectively, sulfur dioxide, TCNE, and oxygen when these gases were adsorbed on γ-irradiated silica gel. As regards sulfur dioxide, a characteristic change in the concentration of the SO2− radical was observed during the post-irradiation with high-energy UV light. In the case of carbon dioxide, the CO2− radical was produced only when UV post-irradiation was added to γ-irradiation. The assignments were principally made in comparison with the reported g-values. Especially, the identification of the CO2− radical was ascertained by using 13C. The analyses of the g-factor for the O2− radical and of 13C hyperfine constants for the CO2− radical gave information on the interaction of the radicals on a solid surface with the cations in the adsorption center. In view of the fact that each of these molecules possesses a different degree of electron affinity, the results described above indicate that the ...