Abstract
The electronic structure of the relaxed exciton is investigated using a Hartree-Fock method. The model concentrates on a cluster of two sodium and two chlorine ions surrounded by an array of point charges. The excited states of the exciton and the associated transitions are discussed. The results are compared with experiment and with the phenomenological models proposed earlier workers. A number of features are confirmed, giving a general picture close to that of Kabler and his co-workers. One problem emerges, since it proves possible to understand the sigma luminescence or the pi luminescence, but not both at present. Possible reasons are discussed. In other respects, there is good agreement with experiment, especially for the optical transitions starting from the lowest triplet state of the exciton.