Bound diffusion of ultrafine particles of ferric hydroxide precipitated inside the polymeric cross-linkage degree the experimental spectra reveal a striking broadening up to hundreds of mm/s. This is a consequence of the crossover from the diffusion of a Brownian oscillator to free diffusion in restricted volume, the spatial displacements of the particles depending on the cross-linkage and changing from 0.1 to 0.6 Å.

We have studied the bound diffusion of ferric hydroxide ultrafine particles imbedded in a solvated polymeric network of Dowex 50W - x1,2 cation exchangers. The Mössbauer experimental data were theoretically treated as continuous diffusion in an arbitrary potential. The shape of this potential was reconstructed from the temperature dependence of the Mössbauer lineshape.