Soft-collision and cusp electrons in longitudinal momentum distributions for single ionization of He and Ne by proton impact

The position of the maximum in longitudinal electron momentum distributions , for He and Ne single ionization by proton impact, has been studied as a f unction of projectile velocity using the continuum-distorted-wave-eikonal-i nitial-state model. At intermediate to high energies the position of the ma ximum is determined by low-energy electron emission and it can be related t o the soft-collision peak. At intermediate to low energies, the position of the maximum depends on the interplay between soft-collision and cusp elect rons, which produces a linear dependence of its position as a function of t he projectile velocity. [S1050-2947(99)51208-0].