Selective Excitation of Triply-Excited States of Three-Electron Ions Observed in Ion-Atom Collisions

Patrick Richard
(J. R. Macdonald Laboratory, Kansas State Univ.)

Triply-excited states have been produced in synchrotron radiation of Li and in low energy ion-atom collisions. The synchrotron radiation studies in general are limited to the studies of low binding energy states and subject to selection rules for photon absorption. The low energy ion-atom collision work typically produces a profusion of excited states via single and multiple electron capture. In the present study we observed triply-excited, three-electron states of ions formed by the dielectronic interaction of two-electron metastable ion beam components with light targets. Projectile electrons scattered in the forward direction are observed in a novel high-efficiency hemispherical detector-analyzer system. A method of enhancing the metastable component of two-electron ion beams was exploited. The electron-ion resonances formed in the collisions were analyzed using the R-Matrix method and found to be in good agreement with experiment. The resonance scattering of target electrons from 1s2s ^3S metastable ions dominantly populates 2s2p^2 ^2D resonances. A second method that is capable of exciting the entire manifold of nlnlnl states was developed. It is based on triple electron capture to high velocity bare ions from selected targets. The Auger spectrum produced by 16 MeV F^9+ ions bombarded on Ar and Kr revealed the 2l2l2l manifold clearly resolved from other structures. Experimental branching ratios and energies were determined. The results were compared with calculations using the hyperspherical close coupling method and the 1/Z expansion.

This work was supported by the Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

Submitted to DAMOP, May 2004 in Tucson, AZ.

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