Energy levels in linear molecules: the inapplicability of Hund's rules

Predictions are made of the relative energies of electronic states arising from various simple electron configurations of linear molecules. It is shown that while empirical generalizations of Hund's rules may sometimes be useful, they are not always applicable, and more useful criteria for assigning states are given. It is believed that the material herein will provide a useful guide to spectroscopists wishing to interpret the electronic spectra of linear molecules.