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 a ccurate X-ray diffraction data has been developed. Dynamical matrix el ements (force constants) for LiH were calculated on the basis of X-ray data. From these force constants, the isotope-reduced partition-funct ion ratio (beta factor) for the LiH (LiD) crystal and the separation f actor alpha(D/H) for the isotope exchange in the solid-gas Li(H,D)-(H- 2,D-2) system have been calculated. The temperature dependence of the isotope separation factor shows good agreement with the experimental d ata.