Observation of the partial decay into H0(n'=2) by excited H- near the n=3 and 4 thresholds

Extreme Correlation and Repulsive Interactions in Highly Excited Atomic Alkali Anions

At high energies, single-photon photodetachment of alkali negative ions populates final states where both the ejected electron and the residual valence electron possess high angular momenta. The photodetached electron interacts strongly with the anisotropic core, and thus the partial cross sections for these channels display non-Wigner threshold behavior reflecting these large, and occasionally repulsive, interactions. Our fully quantum-mechanical theoretical study enables a deeper interpretation of these partial cross sections. Comparisons of the behavior in different channels and between different atomic species-sodium, potassium, and cesium-show the critical role of near degeneracies in the energy spectrum and demonstrate that much of the behavior of the partial photodetachment cross sections stems from the permanent, rather than induced, electric dipole moments of these nearly degenerate channels. This provides a concrete example of a system where negative dispersion forces play a decisive role.

High-resolution vacuum-ultraviolet spectroscopy of an electron-cooled D- beam

The shape parameters for the lowest-lying (1)P(o) resonance, (2)¿0¿-3, of D- have been measured using high-resolution vacuum-ultraviolet spectroscopy. The experiment was performed at the storage ring ASTRID, and the resonance was resolved by applying electron cooling to reduce the velocity spread of the ion beam. The resonance has a width of 37(3) microeV while the asymmetry parameter q of the Fano profile is -16(3). These values present the first critical test of a large number of theoretical calculations.

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.