Zero-degree Auger projectile electron spectroscopy of B2+ in 3-8 MeV collisions with H2

T.J.M. Zouros1,2, E.P. Benis2 and Pat Richard3

1) Department of Physics, University of Crete, Heraklion, Crete, Greece
2) Inst. of Electronic Structure and Laser, FORTH, P.O. Box 1527, 71110 Heraklion, Crete, Greece
3) Dept. of Physics, J.R. Macdonald Lab., Kansas State University, Manhattan, KS 66506-2604

Recently, we have reported on the investigation of electron production mechanisms in H-like and He-like [1, 2] boron ions in collisions with H2 gas targets. The projectile electron spectra were found to result predominantly from the Auger decay of doubly or triply excited [3] states produced by direct capture or resonant elastic/inelastic scattering of quasi-free target electrons off the ions. Here, we follow-up these investigations with a report on electron production in 4-8 MeV collisions of Li-like B2+(1s22s) with H2 targets.

The high resolution spectra for all the boron charge states were recorded at zero-degrees with respect to the ion beam with a mean instrumental energy resolution of 0.2% and an absolute experimental uncertainty in the Auger line energy (projectile rest frame) of 0.6-1.1 eV. The three electron spectra for B2+ collisions with H2 are shown in Fig. 1. The Be-like 1s2s2p2 3,1D lines are known to be produced by resonant elastic scattering off the B2+ ion of the quasi-free H2 electrons. These lines go through a maximum at the ion collision energy of 3.8 MeV. The Li- like (1s2s)2p 2P- and 1s2p2 2D lines are produced by direct excitation. The energies of higher- lying KLn lines (c1-c10) have been compared to Hartree-Fock calculations using the Cowan code. Our analysis shows most of these lines can be assigned to Li-like 1s2lnl" states with n = 3 - 4 Auger decaying to the B3+(1s2) ground state. The proposed intermediate states, the Auger electron energies resulting from their decay to the ground state, and the most probable production mechanisms are discussed.

Figure 1: Absolute electron double differential cross sections (DDCS) for 3.70, 5.76 and 7.95 MeV collisions of B2+(1s22s) with H2. The production of the 2S, 4P, 2P-, 2P+ and 2D Li-like doubly excited states is most prominent. The Be-like doubly excited states (1s2s2p2)3D and (1s2s2p2)1D are also observed. Higher-lying KLn lines (c1-c10) are scaled for improved presentation as indicated.


[1] T. J. M. Zouros, E. P. Benis and T. W. Gorczyca, 68, 010701(R) (2003).
[2] E. P. Benis, T.J.M. Zouros, T. W. Gorczyca, A. D. González and P. Richard, Phys. Rev. A 69, 052718 (2004).
[3] E. P. Benis, T. J. M. Zouros, T. W. Gorczyca, M. Zamkov, and P. Richard, J. Phys. B 36, L341-L348 (2003).

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 ICPEAC, July 2005 in Rosario, Argentina.

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