Resonances in low-energy electron scattering on atomic Rb, Cs, and Fr

U. Thumm
Dept. of Physics, Kansas State University, Manhattan, KS

C. Bahrim
Dept.s of Physics, Kansas State University and Lamar University, Beaumont, TX

I. I. Fabrikant
Dept. of Physics and Astronomy, University of Nebraska, Lincoln

Within the relativistic Dirac R-matrix method and a model based on an effective two-electron approach¹, we analyze the spectra of Rb^-, Cs^- and Fr^- ions in electron scattering by Rb, Cs and Fr targets at incident electron energies below 2.8 eV. Our calculations predict the same ³P^o,e, ³F^o and ¹P^o resonances for all three anions² in calculations of angle-dependent, momentum transfer, and total cross sections. We discuss relativistic effects in the resonance profiles. Our 1⁺ partial cross sections show pronounced Ramsauer-Townsend (RT) minima at 41/46/32 meV for Rb/Cs/Fr, caused by the strong atomic polarizability and related to a ³S^e virtual state³ . In the total converged cross section these RT minima are shifted to lower energies (4.6/1.1 meV for Rb/Cs, and below 1 meV for Fr) due to the nearby ³P^o resonance. We also discuss our spin-flip and spin-exchange cross sections for e^- + Rb, Cs and Fr collisions in comparison with experimental data.

References:

[1] U. Thumm and D.W. Norcross, Phys. Rev. A 45, 6349 (1992)
[2] C. Bahrim, U. Thumm and I.I. Fabrikant, Phys. Rev. A 63, 042710 (2001);
C. Bahrim and U. Thumm, Phys.Rev.A 64, 022716 (2001)
[3] C. Bahrim, U.Thumm, and I.I. Fabrikant, J. Phys. B 34, L195 (2001)

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 GEC02, October 2002 in Minneapolis, MN.

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