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Coulomb four-body problem: electron-impact double ionization of helium in the threshold regime
Xueguang Ren1, Alexander Dorn, Joachim Ullrich
1Max-Planck-Institute for Nuclear Physics, 69117 Heidelberg, Germany.
Abstract:
Double ionization of helium by electron impact is studied in a kinematical complete experiment in the threshold regime at 5 eV excess energy. As expected the recoil ion carries the full initial projectile momentum and the emitted electrons' sum momentum in average is zero. The electron emission is revealed to be completely dominated by the symmetric 120 degrees configuration predicted by many threshold theories but never observed experimentally before. Fully differential cross sections show a more complex structure than expected for a pure threshold collision dynamics.
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