Almost bound states of heavy negative akali ions

Almost bound states of heavy negative akali ions

Uwe Thumm
Dept. of Physics, Kansas State University, Manhattan, KS 66506

In collaboration with Cristian Bahrim (Lamar University, TX) and Ilya Fabrikant (University of Lincoln, NE).

Based on the Dirac R-matrix method [1], a relativistic generalization of the effective range theory [2], and a boundary-corrected Pauli equation (PE) approach [3], I will discuss the spectra of Rb^-, Cs^-, and Fr^- anions in electron scattering [4] and photodetachment [3]. For incident electron energies below 2.8 eV, our calculated angle-differential, momentum-transfer, and total scattering cross sections predict the same ³P^o,e , ³F^o, and ¹P^o resonances for all three anions. Our J^π = 1⁺ partial cross sections show pronounced Ramsauer-Townsend minima at 41/46/32 meV for Rb/Cs/Fr which are caused by the large atomic polarizabilities and are related to ³S^e virtual states [2]. I will discuss relativistic effects in the resonance profiles and review our spin-flip and spin-exchange cross sections for slow e^- + Rb, Cs, and Fr collisions in comparison with experimental data. By integrating the PE using an effective potential that is adjusted to reproduce scattering phase shifts provided by exact Dirac R-matrix scattering calculations [4], we calculated angle-differential and total photodetachment (PD) cross sections [3]. In order to avoid an unphysical singularity of the standard PE, we formulated an appropriate boundary condition near the nucleus based on the exact solution of the Dirac equation for a Coulomb potential. Our ³P^o₁ resonance contribution to the PD cross section of Cs^- agrees (in position and width) with recent experiments [5].

References:

[1] U. Thumm and D.W. Norcross, Phys.Rev.A 45, 6349 (1992).
[2] C. Bahrim, U.Thumm, and I.I. Fabrikant, J. Phys. B 34, L195 (2001).
[3] C. Bahrim, I.I. Fabrikant, and U. Thumm, Phys.Rev.Lett. 87, 123003 (2001).
[4] C. Bahrim, U, Thumm, and I.I. Fabrikant, Phys.Rev. A 63, 042710 (2001);
Phys.Rev. A 64, 022716 (2001).
[5] M. Scheer et al., Phys.Rev.Lett.80, 684 (1998).

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.

Invited talk submitted to GEC02, October 2002 in Minneapolis, MN.

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