Introducing thermal effects in the rotational energy of diatomic molecules

At relatively high temperatures, the state-of-the-art of the diatomic liquid phononic theory applied to super-critical fluids shows that there exists discrepancies between the theoretical predictions and the experimental data. To overcome this difference, a new formulation of the rotational energy of single molecules that considers the thermal effect upon their moment of inertia, is presented. For a wide range of reduced temperatures and pressures, the predicted values are in very good agreement with CO, O-2 and N-2 molecular data. It is possible to reduce these discrepancies by a factor of 2 up to around 70 times for some cases. This is essentially because the proposed model improves the rotational energy of the molecule. It implicitly satisfies both the Dulong-Petit law for ideal gases as well as the Frenkel's line thermodynamic limit.