Electrons ejected with half the projectile velocity and the saddle point mechanism in ion-atom collisions
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.
Sidky
EY
Department of Physics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506, USA.
Illescas
C
Lin
CD