Mössbauer Absorption in Overdamped Harmonically Bound Particles in Brownian Motion

Recent Mössbauer studies of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in a variety of biological systems, including proteins and membranes, reveal absorption spectra consisting of a narrow "elastic" part and a wide "inelastic part." These results are interpreted here by a model of bounded diffusion in which overdamped harmonically bound particles are in Brownian motion. Excellent fits to experimental data are obtained, which yield values of the mean square displacement $〈x^2〉$ and diffusion coefficient $D$ of the particles.