The Ratio D _int /D between the Coefficients for the Diffusion of Internal Energy and of Self Diffusion in Thermal Conductivity Data Correlations for Gases of Linear Molecules

Highly consistent sets of generalized cross sections are used to judge critically correlations of the thermal conductivity in the limit of zero density for nitrogen, carbon monoxide, and carbon dioxide. The correlations were developed by Millat, Vesovic, and Wakeham some years ago using restricted experimental information in order to deduce a set of generalized cross sections as consistent as possible for the extrapolation beyond the temperature range of the primary experimental data. Recently, the generalized cross sections needed have been evaluated by means of classical trajectory calculations for rigid rotors on the basis of accurate anisotropic ab initio potential energy hypersurfaces including a new improved way to take into account the vibrational degrees of freedom. It is shown that the ratio between the coefficients of internal energy and of self diffusion D_int /D was not appropriately chosen and that this effect was extensively compensated in a fortuitous way in the course of the development of the data correlations by a likewise unsuitable choice of the ratio A* between the effective cross sections of viscosity and self-diffusion.