Calculation of thermodynamic properties of solids from accurate diffraction data: isotope separation factor in systems containing crystalline phase

A method of calculation of the thermodynamic partition function from accurate X-ray diffraction data has been developed. Dynamical matrix elements (force constants) for LiH were calculated on the basis of X-ray data. From these force constants, the isotope-reduced partition-function ratio (β factor) for the LiH (LiD) crystal and the separation factor αD/H for the isotope exchange in the solid-gas Li(H, D)-(H2, D2) system have been calculated. The temperature dependence of the isotope separation factor shows good agreement with the experimental data. (orig.)