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 Schrödinger 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.