Thermodynamic functions of molecular hydrogen from ab Initio energy levels

A tabulation is presented of the thermodynamic properties of molecular hydrogen (H₂, D₂ and HD), calculated using energy levels which had been obtained via a solution of the Schrodinger equation. The present results should be more accurate than prior computations based on spectroscopic extrapolation formulae. They provide the first example of an accurate determination of a bulk, macroscopic property directly from first principles (input: masses and Coulomb’s law). The results are tabulated for ortho, para, the equilibrium and the frozen (or normal’) mixture (3: 1 for H₂, 1: 2 for D₂) over the temperature range 5–300 K and for the frozen mixture up to 6000 K. The importance of anharmonicity and of quasi-bound levels at high temperatures is discussed.