Nonadiabatic selection rules for the photoabsorption of H- and He

Wannier-ridge states of He and H(-) with symmetries (3)P(e) and (1)D(o) and the validity of classification schemata

High lying doubly excited Wannier-ridge states of He and H(-) with symmetries (3)P(e) and (1)D(o) are studied and energies and intrinsic characteristics of their wave functions are reported. Energies of these states associated with the hydrogenic threshold up to N=20 are presented and, wherever available, we compare them to other calculations. Proposed classification schemata for these states by approximate collective quantum numbers are examined.

Excitation and decay of correlated atomic States

Doubly excited states of atoms and ions in which two electrons are excited from the ground configuration display strong radial and angular electron correlations. They are prototypical examples of quantum-mechanical systems with strong coupling. Two distinguishing characteristics of these states are: (i) their organization into successive families, with only weak coupling between families, and (ii) a hierarchical nature of this coupling, with states from one family decaying primarily to those in the next lower family. A view of the pair of electrons as a single entity, with the electron-electron repulsion between them divided into an adiabatic and a nonadiabatic piece, accounts for many of the dominant features. The stronger, adiabatic part determines the family structure and the weaker, nonadiabatic part the excitation and decay between successive families. Similar considerations extend to three-electron atomic states, which group into five different classes. They are suggestive of composite models for quarks in elementary particle physics, which exhibit analogous groupings into families with a hierarchical arrangement of masses and electroweak decays.

The semiclassical helium atom

Recent progress in the semiclassical description of two-electron atoms is reported herein. It is shown that the classical dynamics for the helium atom is of mixed phase space structure, i.e., regular and chaotic motion coexists. Semiclassically, both types of motion require separate treatment. Stability islands are quantized via a torus-quantization-type procedure, whereas a periodic-orbit cycle expansion approach accounts for the states associated with hyperbolic electron pair motion. The results are compared with highly accurate ab initio quantum calculations, most of which are reported here for the first time. The results are discussed with an emphasis on previous interpretations of doubly excited electron states