Use of Model Potentials in the Study of Molecular Rydberg States

In this paper we investigate the applicability of simple model potentials containing adjustable parameters to the description of molecular Rydberg states. Qualitative criteria for the selection of appropriate potentials are discussed and the results of numerical calculations relevant to the Πu3 states of H2, the Σu1(2Σgcore) states of N2, and some Rydberg states of benzene are presented. It is found that the model potentials proposed adequately describe the effective potential of the positively charged core in the Rydberg states. In the case of benzene, a unique assignment of the experimentally observed Rydberg series is impossible because of the ambiguity of the calculated term values arising from the adjustable parameters in the potential. We also discuss the limitations of semiempirical potentials and suggest the use of model potentials that contain no adjustable parameters.