A rotor molecule in an atomic cryomatrix. Indirect impurity interaction

A theory of indirect static interaction of dumbbell-shaped impurities in an atomic matrix (like N2 in Ar) is constructed in the framework of the theory of elasticity. The presence of impurity ensembles round a chosen impurity entails random tetragonal distortions (over the ensemble) in the local vicinity of the chosen impurity and, as a consequence, an additional splitting of the Devonshire spectrum. The phonon-rotational coupling constants and the intensities of the relevant interactions (in particular, the partial coefficient describing the response of the rotor to the elastic deformation field around a dilatation center) are evaluated by using the known intermolecular potentials for N2 and CO as impurities and Ar, Kr, and Xe as matrices. The thermodynamics of statically interacting impurities is constructed by taking into account the fact that the influence on the chosen impurity depends weakly on the rotational state of the impurity exerting it. The parameters determining the statistics of the Devonshire spectrum splitting for the N2 in Ar system are evaluated and the shape of the line describing thermodynamic transitions contributing to the low-temperature heat capacity is determined. The role of the direct rotor-rotor interaction in the thermodynamics of these systems is discussed.