Resonance structure in the Li- photodetachment cross section

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.

K-shell photodetachment of Li(-): experiment and theory

An experimental K-shell photodetachment study of Li(-) giving rise to doubly photoionized Li(+) ions has been carried out at the Advanced Light Source, using a collinear photon-ion beam apparatus. The experiment reveals dramatic structure, differing substantially both qualitatively and quantitatively from the corresponding processes above the 1s ionization threshold in Li and Li(+), as predicted by our enhanced R-matrix calculation. The experimental/theoretical comparison shows good agreement over some of the photon energy range, and also reveals some puzzling discrepancies.

Spectrum of doubly excited states in the K- ion

The energies and widths of doubly excited states of the K- ion in the vicinity of the K(5 2D,7 2S,5 2F) thresholds have been measured in high resolution using a sensitive collinear laser-ion beam apparatus. These transient states appeared as resonances in the partial cross section for photodetachment via the K(5 2S)+e(-)(epsilon(p)) channel. Series of two states below the 5 2D threshold and four states below the 5 2F threshold have been found. The relative widths of members of the series below the 5 2F threshold exhibit anomalous behavior, as predicted by a semiclassical model.

Autodetachment of doubly excited states in nonhydrogenic negative ions

A semiclassical model is developed to describe the two-electron dynamics of the process of autodetachment. A formula derived for the partial width of a doubly excited state represents a product of an amplitude and phase factors. An anomalous width behavior is predicted for states near a threshold when the orbital angular momentum of the outer electron is high. Oscillations of the phase factor, as a function of energy, determine the functional behavior of relative widths in the region farther from threshold for a given series of states.