The Librational Heat Capacity of Ice and of Heavy Ice

Abstract

Interpretation of the heat capacities of crystals is difficult when polyatomic molecules or ions are involved, owing to the variation with temperature of the translational heat capacity, arising from intermolecular vibrations, in the same regions in which rotational and vibrational heat capacities are also varying with temperature. It is shown how translational and rotational heat capacities may be studied separately in the case of ice where the heat capacities of both H2O and D2O have been measured. Moments of inertia are nearly doubled by substitution of D for H, while the molecular weight is increased by only ten percent. Thus the effect of isotopic substitution is relatively large on the rotational heat capacity as compared to the translational heat capacity.