Heat Capacity Curves of the Simpler Gases. VI. Rotational Heat Capacity Curves of Molecular Deuterium and of Deuterium Hydride. The Equilibrium Between the Ortho and Para Forms of Deuterium. Free Energy, Total Energy, Entropy, Heat Capacity and Dissociation of H2H2 and of H1H2, to 3000°K1

Abstract

Heat capacities, entropies, free energies, total energies and dissociation constants have been calculated for H²H² and for H¹H², to 3000°K, by reliable methods and are listed in tabular form. The ortho‐para equilibrium in H²H² has been considered for both the gaseous and the solid states. The solid state equilibrium has been discussed from the point of view of its bearing on the application of the third law of thermodynamics. The rotational heat capacity curves of the various forms of H²H² and that of H¹H² are shown graphically and are compared with the rotational heat capacity curve of ordinary hydrogen and with the hypothetical rotational specific heats of gaseous nitrogen. The heavy molecules, H²H² and H¹H², dissociate to only about one‐half the extent of H¹H¹ below 3000°K. The three hydrogen molecules are compared with respect to the influences of molecular stretching and of anharmonic vibration in the high temperature heat capacities. We also include tables which show the distributions of molecules among the vibrational levels as a function of the temperature.