Effective cross-sections for the thermal conductivity of diatomic gases

A new improved way for the inclusion of the vibrational degrees of freedom into the calculation of the thermal conductivity of dilute gases of diatomic molecules is proposed and has been tested for nitrogen and carbon monoxide. The effective cross-sections needed have been obtained using classical trajectory rigid-rotor calculations following the procedure by Heck and Dickinson on the basis of anisotropic ab initio potential energy hypersurfaces of both molecules. The calculations have been performed for the second-order approximation of the kinetic theory including corrections for the polarization effects of the rotational angular momentum according to Kagan and Maximov. The vibrational energy states have been taken into account by suitably chosen corrections of the effective cross-sections needed in the first-order approximation of the kinetic theory. In particular, the effective cross-section for the vibrational energy has been neglected, whereas the effective cross-section for the vibrational energy flux has been approximated by the effective cross-section for the particle flux connected with the self-diffusion coefficient.