Molecular rotator in an atomic inert-gas matrix. Quasistatic renormalizations

A microscopic calculation of the relaxational renormalization of the crystal field, acting on a molecular rotator in the matrix of an atomic inert-gas crystal, is carried out in the quasistatic approximation. It is shown that the relaxation of the lattice around the rotator does not alter the symmetry of the crystal field. The renormalized crystal field constant is calculated; the renormalization is significant, and for specific systems (N2 and CO impurities in Ar, Kr, and Xe matrices) equals 1.6–1.7. The concept of a cubic order parameter, which can be employed as a quantitative characteristic of the degree of rotational localization (hindrance) in a field with cubic symmetry is introduced. The tunneling approach to the rotational dynamics of a molecular rotator is formulated for the low-energy part of the spectrum. The tendency for the rotational constant to be renormalized is determined in a rough approximation. The effect of renormalization on the heat capacity and thermal expansion of atomic inert-gas matrices with diatomic impurities is discussed.

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