High-Temperature and Nonequilibrium Partition Function and Thermodynamic Data of Diatomic Molecules

Accurate molecular partition functions are required to determine both thermodynamic properties for equilibrium and nonequilibrium flow field calculations, and energy level populations for radiative heat transfer in high enthalpy flows, for instance. Thermodynamic functions of diatomic molecules are computed in this study at high temperatures and for nonequilibrium media in the framework of multi-temperature models. Partition functions, average energies, and specific heats of N(2), N(2)(+), NO, O(2), CN, C(2), CO, and CO(+) are calculated up to 50,000 K by direct summation over energy levels using recent and accurate spectroscopic data and dissociation energy values. Estimates are made for the error introduced by neglecting the highest considered electronic states. For nonequilibrium media, the sensitivity of the multi-temperature thermodynamic functions to different schemes for energy partitioning is discussed. In particular, the effects of vibration-rotation coupling are investigated. The tabulated results are available upon request.