A rotor molecule in an atomic cryomatrix. I. Excess dilution volume
Abstract
The problem of excess dilution volume of an isotropically dilating impurity is considered as a part of a more general problem of dilatation around a dumbbell impurity in an atomic lattice. Displacements u of neighboring atoms are calculated from static equilibrium conditions so that the values of u on the nine nearest coordination spheres are regarded as unknown, and the displacement on next spheres are taken equal to the values obtained in the long-wave approximation. A relation between the atomic displacement in the first sphere, the excess dilution volume ΔV and the extra force exerted by an impurity on the nearest neighbor is established. It is shown that the thermal variation of dilution volume from a temperature of about 10 K to the melting temperature is almost entirely due to a change in the normalization parameter (equal to the ratio of F to the elastic modulus) caused by the thermal variation of the lattice parameter. A comparison based on the previously suggested interaction potentials between N2 and CO impurities and Ar, Kr and Xe atoms shows a good agreement with x-ray data.