Electron paramagnetic relaxation in aqueous solutions of manganese (II) ions

Abstract

The processes of the electron paramagnetic relaxation, molecular motions and structural changes in aqueous solutions of manganese nitrate have been investigated by direct measurement of spin-lattice (T 1) and spin-spin (T 2) relaxation times for a wide range of concentrations, temperatures and viscosities. T 1 and T 2 were measured by a non-resonance absorption method. It was discovered that some structural regions exist at the different concentrations of Mn(II) ions in solution. So, the structure of highly concentrated solutions may be considered as one of the corresponding crystallohydrate. The structural microinhomogeneities were observed also in the intermediate concentration range at definite temperatures. It is shown that the relaxation mechanism proposed by Bloembergen and Morgan is not effective in the concentration range studied by us. The analysis of relaxation times and E.P.R. spectra has shown the formation of ‘liquid microphases’ at the freezing point of the solution. Such microphases can exist at temperatures a few tenths of a degree below the solvent freezing point, and its composition considerably differs from the initial solution. The correlation times for intramolecular and intermolecular electron relaxation mechanisms are evaluated and their nature is discussed.