New studies of the mechanism of electron emission at zero degrees in collisions of 100 keV protons with H2and He

Measurements of double differential cross sections for electron emission at zero degrees arising from collisions of 100 keV protons with H 2 and He have been carried out. Calculations based on a continuum-distorted-wave eikonal-initial-state model have also been carried out and shown to provide a good description of the measurements. In addition, classical-trajectory Monte Carlo calculations have been employed to illustrate the evolution of electron emission at different times during the collision. The present measurements, which use a well defined gas target, provide no evidence of the existence of a significant saddle-point ionization mechanism at the energy considered.