RYDBERG LEVELS OF THE SODIUM ATOM AND THE AMMONIUM RADICAL CALCULATED BY PERTURBATION THEORY.

Rydberg levels of sodium and the ammonium radical have been comptued by second-order Rayleigh-Schroedinger perturbation theory with the frozen-core model defining the zero-order problem. Very extensive basis sets are used. From the sodium atom study, the authors determine the contributions of f- and g-type functions to the pair correlation energies and use this information to correct for basis set deficiencies as well as higher perturbation corrections in the molecular problem. The theory supports J. K. G. Watson's assignment of the Schueler band as being the analogue of the sodium D line, and implies that this is also the most likely assignment of the Schuster band.