Users publish findings on "Lithium inner-shell resonances in the 70–77 eV photon energy region"
Authors: D Lukic, SB Whitfield, and R. Wehlitz
Helium is not only a textbook example for double ionization but also for double excitations because it is a simple two-electron system. Double excitation is due to electron correlation because two electrons are actively involved in this process stimulated by only a single photon. Double-excited states of a low-Z atom typically autoionize where one electron is emitted while the second electron falls back into a lower shell. This leads to resonance profiles ("Fano profiles") in the single-ionization cross section.
Lithium is a slightly more complex system than He as there is a third electron in the atom, which is, at least, a spectator in the autoionization process. Thus, autoionization of the Li 1s3lnl' doubly-excited states appear to be similar to the He 3lnl' doubly-excited states except for the additional 1s electron, which makes theoretical calculations more complicated. Therefore, experimental data can provide a stringent test of the quality of such calculations.
In our recent paper we present a high energy resolution study of the Li 1s3lnl' (l=s,p,d; n >= 3) inner-shell resonances, which are arranged in six Rydberg series. Employing the PGM beamline with a resolving power of 13,000 we have tracked the autoionizing resonances to higher principal quantum numbers than in previous experiments. Using Fano profiles to fit our ion yield spectra we have determined the positions, widths and profile parameters of the resonances. From the resonance positions we have derived the series limits and quantum defects of six Rydberg series. We find very good agreement with the resonance positions and widths of R-matrix calculations.
The paper can be found online at: http://www.iop.org/EJ/abstract/0953-4075/42/8/085004/.