Classification scheme of triply excited states from a molecular viewpoint

Energy levels of triply excited states of an atom with all three electrons in the same shell are obtained by a model calculation. The nodal pattern of an eigenfunction at the symmetry configuration plays a crucial role in the manifestation of moleculelike modes as in the case of doubly excited states. It is shown that the correlation of the three electrons leads to normal modes isomorphic to those of a molecule with $D_{3h}$ symmetry. The energy levels may be thus regrouped into manifolds, each revealing the rotational level structure of a symmetric top. The validity of the model is discussed in reference to known experimental and theoretical results.