The Transport Properties of Sodium Atoms and the Heat Capacity of Sodium Dimers at High Temperatures


Including the contribution of excited state atoms can improve calculations of dilute gaseous transport properties at high temperatures. For sodium, experimental and/or theoretical information is available about the potential energy curves associated with each of ten low-lying states of the sodium dimer. These include the X 1 Σ g + and 3Σ u + states that dissociate to two ground state 2S sodium atoms and the four 3Σ g,u +, 1Σ g,u +, 1Π g,u, 3Π g,u gerade/ungerade pairs of states that dissociate to a ground state 2S atom and an excited state 2P atom. Nine of these are bound states and have been fitted with the Hulburt-Hirschfelder potential, a very good general purpose atom-atom potential. The 3Π g state is not bound and has been fitted with the exponential repulsive potential. We have used these potentials to calculate viscosity collision integrals as a function of temperature, and employed degeneracy-weighted averaging to determine the viscosity and translational contribution to the thermal conductivity of the sodium atoms. These same potentials have been used to calculate the heat capacity, C p o, of the sodium dimer using an approach that depends on the second virial coefficient and its first two temperature derivatives. Again, the inclusion of molecular states that dissociate to an excited state atom allows C p o to be determined with improved accuracy at higher temperatures. Thus, thermophysical property calculations for sodium have been extended to 25,000 K. These results are compared with previous results, including heat capacities given in the NIST-JANAF Thermochemical Tables. © Springer Science+Business Media, LLC 2010.



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