Thermochemical properties of atoms and molecules in specific quantum states

Abstract

Procedures are described for computing thermochemical properties in the ideal gas state for atoms and molecules in specific quantum states, and in thermal or nonthermal distributions over specific groups of quantum states. Formulas are given to generate values in the JANAF-compatible format. Applications to electronic states of atoms, vibrational and vibration–rotational states of diatomic molecules, and vibrational states of polyatomic molecules are given as illustrations. It is shown that the choice of procedure for obtaining partition functions has only a minor effect upon the accuracy of the results, the major factors being the energy of the specified state(s) and the accuracy to which the heat of formation of the species itself is known. Procedures are developed for describing systems in which species in specified quantum states are considered together with the same species in a Boltzmann internal distribution, and for expressing the thermochemical properties of state-selected species as polynomials in temperature.