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Electrons ejected with half the projectile velocity and the saddle point mechanism in ion-atom collisions
1Department of Physics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506, USA.
Abstract:
Full three-dimensional ejected electron momentum distributions for proton impact ionization of atomic hydrogen are calculated for impact energies 10 through 50 keV. The distributions show a peak in the longitudinal momentum at half the projectile impact velocity: the v/2 peak. A quantitative assessment of saddle point ionization, based on quantum and classical analysis, reveals that the v/2 peak is a false indicator for this mechanism. The influence of the potential saddle on ionization is seen to decrease rapidly from 10 to 50 keV.
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