Thermodynamic properties of clathrates

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Abstract
Measurements have been made from a temperature between 14 and 20°k to ∼300°k of the heat capacity of three carbon monoxide quinol clathrates, two oxygen quinol clathrates and one nitrogen quinol clathrate. The results have been used to estimate the contribution C A made to the heat capacity by a mole of carbon monoxide, nitrogen or oxygen in the clathrate. Analysis of the C A values leads to the conclusion that the barrier hindering rotation of the molecules in the cavities is ∼200 cal mole-1 for oxygen, ∼1100 cal mole-1 for nitrogen and slightly larger for carbon monoxide than for nitrogen. Possible reasons for these differences are briefly discussed. An attempt has been made to calculate the heat capacity contribution of the trapped molecules at low temperatures where a classical treatment is no longer applicable. The agreement with experiment is not good, which may be due party to the alteration of the heat capacity of the lattice itself by the trapped molecules, and partly to the inadequacy of the potential energy function used in the calculations.