The heat capacities of atoms are calculated from the atomic partition function, q, and its temperature derivatives.There are over 230 experimental electronic energy states of oxygen atoms listed in the NIST Atomic Spectra Database (ASD) at energies lower than that of the first ionization potential. These states contribute to the electronic partition function. At low and intermediate temperatures, the more highly excited electronic states make essentially no contribution to q but, at higher temperatures, the excited states contribute significantly to q which becomes larger as the temperature increases. Thus the calculated values of the heat capacity also increase, often to very large values that are unlikely to be correct. In addition, the enegies of many electronic states are not known. In fact, there should be a very large number of electronic states with energies less than that of the first ionization potential. Thus it should be expected that calculated values of heart capacities should get very large. This means that some criteria must be found to limit the sum over excited electroniuc states in q. Two methods for doing this, one based on intermolecular forces and the other based on the excluded volume, are used to calculate the heat capacity of oxygen atoms at high temperatures.

Heat capacity of oxygen atoms at high temperatures

249th National Meeting (2015)

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