Mössbauer effect and molecular motion in condensed systems with diffusion

Mössbauer effect in solutions of FeSO₄, 7H₂O and Na₂[Fe(CN)₅NO], 2H₂O in CH₂OH-CH₂-CH₂OH has been investigated. Areas, line widths, isomer shifts and quadrupole splittings are determined as functions of temperature in both the supercooled liquid state and the polycrystalline state. Phase transformations show up in all four parameters. We discuss the customary interpretations of areas in terms of 〈x ²〉 _T for rapid oscillatory motion and line widths in terms of the diffusion coefficientD. An unexpected linear dependence ofD on 〈x ²〉 _T found experimentally is shown to be in accordance with a model expression presented for the velocity autocorrelation function.