The ESR Study of the Interaction of O2 with Ag Dispersed on Silica Gel

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Abstract
The state of adsorbed oxygen on metallic silver dispersed on silica gel has been studied by ESR. The spectra observed by the interaction of oxygen and the surface were found to be composed of spectra due to two different species. One of the species, which was formed separately by the contact with oxygen at −110 °C, was identified with O2− chemisorbed on metallic silver by a comparison of the observed g values and the other features with those previously reported. The other species has a doublet at g=2.036. This spectrum was reproduced by the interaction of N2O with the silver surface. Further, the γ-irradiation of the silver samples in the presence of O2 and N2O markedly enhanced the intensity of this spectrum, showing a low-field hump. On the basis of the g values and the splitting of the high-field doublet, assuming that the doublet is due to the hyperfine interaction of an unpaired electron with the silver nucleus, the species was assigned to Ag2+ in the present system. It is postulated that this species is possibly formed by the dissociative and/or charge-transfer chemisorption of O2 and N2O, suggesting the presence of non-paramagnetic oxygen species, such as O2−, as a counter ion of Ag2+.