Hindered rotation of linear molecules in atomic cryocrystals and the thermal properties of solutions

The heat capacity and thermal expansion of Ar and Kr crystals as well as of the solid solutions of nitrogen isotopes based on them are studied in the temperature range 2−12 K. The impurity concentration varied from 0.5 to 2 mole %. The study of the system revealed an anomalous behavior of the thermal properties of the solutions owing to the unhindering of the rotational degrees of freedom of the impurity molecules. The results obtained are interpreted on the basis of the Devonshire–Manz–Mirsky (DMM) model. The barriers hindering the rotation of impurity molecules in Ar and Kr matrices are determined. It is predicted that a low-temperature peak exists in the heat capacity of the solutions with maxima in the region T < 1 K and that the coefficient of thermal expansion is negative below 1 K.

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