Supermultiplets in doubly excited atoms

Take an excited hydrogen atom, add a second excited electron, and you change the calculation of energy levels from an easy problem to a formidable task. In such doubly excited atoms, the dominance of electron correlations considerably alters the single‐particle shell structure. Alternative formulations of the electronic states in terms of hyperspherical coordinates have greatly elucidated the angular and radial correlations. That progress was recently boosted by the insight from dynamical group theory: A supermultiplet classification gives striking order to the energy spectrum and predicts which electron states become mixed. This supermultiplet classification visually depicts the doubly excited atom as a linear triatomic molecule having the electrons across the nucleus from one another and exhibiting collective rotational and bending motions. This new view is compatible with that of the hyperspherical approach. All the varying perspectives were discussed last month at the meeting of the APS Division of Electron and Atomic Physics in New York.

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