Narrow chaotic compound autoionizing states in atomic spectra
- School of Physics, University of New South Wales, Sydney 2052 (Australia)
Simultaneous excitation of several valence electrons in atoms gives rise to a dense spectrum of compound autoionizing states (AIS). These states are almost chaotic superpositions of large numbers of many-electron basis states built of single-electron orbitals. The mean level spacing {ital D} between such states is very small (e.g., {ital D}{lt}0.01 eV for the numerical example of {ital J}{sup {pi}}=4{sup {minus}} states of Ce just above the ionization threshold). The autoionization widths of these states estimated by perturbations, {gamma}=2{pi}{vert_bar}{ital W}{vert_bar}{sup 2}, where {ital W} is the Coulomb matrix element coupling the AIS to the continuum, are also small, but comparable with {ital D} in magnitude: {gamma}{approximately}{ital D}. Hence the nonperturbative interaction of AIS with each other via the continuum is very essential. It suppresses greatly the widths of the autoionizing resonances ({Gamma}{approx_equal}{ital D}{sup 2}/3{gamma}{lt}{ital D}), and leads to the emergence of a {open_quote}{open_quote}collective{close_quote}{close_quote} doorway state which accumulates a large share of the total width. This state is in essence a modified single-particle continuum decoupled from the resonances due to its large width. Narrow compound AIS should be a common feature of atomic spectra at energies sufficient for excitation of several electrons above the ground-state configuration. The narrow resonances can be observed as peaks in the photoabsorption, or, in electron-ion scattering, as Fano-type profiles on the background provided by the wide doorway-state resonance. It is also shown that the statistics of electromagnetic and autoionization amplitudes involving compound states are close to Gaussian. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 383137
- Journal Information:
- Physical Review A, Vol. 54, Issue 3; Other Information: PBD: Sep 1996
- Country of Publication:
- United States
- Language:
- English
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