Abstract
The paper deals with the study of the spectra of the electron paramagnetic resonance (EPR) of the Mn2+ ions adsorbed on the silica gel. Further on there have been studied the changes in the EPR spectrum of the Mn2+ ions adsorbed on the silica gel that are occuring as a result of dehydratation of the introduced samples, as well as the spectra changes of these samples that have arisen owing to the natural adsorption of the water vapour from the air under normal physical conditions.
At low concentrations of the Mn2+ ions adsorbed on the silica gel, the EPR resonance spectrum contains six hyperfine structure (HFS) components the widths of which enlarge towards higher magnetic fields and do not change with the increase of the Mn2+ ions concentration.The spectrum further contains a system of lines that have been identified as the so-called “forbidden” transitions, when simultaneously with the orientation of the electron spin the orientation of the nuclear spin changes as well. This spectrum corresponds to the Mn2+ ions adsorbed in the individual positions considerably far from each other, without mutual dipole-dipole interaction.
During further increase of the adsorbed Mn2+ concentration, there appears in the EPR spectrum, besides the above-described HFS, a broad symetric line the width of which does not change with increasing concentration, except for high concentrations when it becomes narrower probably due to the exchange interaction. This signal corresponds to the Mn2+ ions adsorbed in clusters, probably in the silca gel pores, when the HFS gets smudged as a result of dipole-dipole interaction.
It appears that the width of the EPR spectrum broad line is dependent upon the temperature at which the dehydratation process was passing. At the adsorption of water vapour from the air under normal conditions on the dehydrated sample, there arise expressive changes in the EPR spectrum shape. The broad line decomposes in 6 HFS components, the widths of which change with duration time of the water vapour adsorption. Since the HFS of the individually adsorbed Mn2+ ions does not change after the dehydratation and the ensuing water vapour adsorption, the EPR spectrum of these samples becomes a superposition of two hyperfine structures coresponding to the two inequivalently bound groups of Mn2+ ions.
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Hronský, V., Rákoš, M., Belák, J. et al. EPR study of Mn2+ ions adsorption on silica gel. Czech J Phys 28, 1277–1286 (1978). https://doi.org/10.1007/BF01599967
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DOI: https://doi.org/10.1007/BF01599967