Electron-Spin-Resonance Study of High-Concentration Manganese Nitrate Aqueous Solutions

The electron spin resonance (ESR) of manganese nitrate aqueous solutions was studied over the concentration range 3.5 × ${10}^{-3\mathrm{}}$-8.25 mole/liter. ESR and viscosity data were obtained from 20 to 90 °C. The spectrum exhibited six well-resolved hyperfine components at low concentrations which transformed to a partially exchange-narrowed singlet at high Mn (II) concentrations. Collapse of the hyperfine structure (hfs) was analyzed from computer-synthesized spectra whose component linewidths and positions were obtained from Anderson's theory of exchange narrowing. It was found that exchange-narrowed spectra of Mn (II) ions were described by Anderson's case (b), in which transitions occur only between adjacent hyperfine components.