Low-Energy Electrons and Their Dynamical Correlation with Recoil Ions for Single Ionization of Helium by Fast, Heavy-Ion Impact.

Helium single ionization by 3.6 meV/u Ni[sup 24+] impact was explored in a kinematically complete experiment by combining a high-resolution recoil-ion momentum spectrometer with a novel 4[pi] low-energy electron analyzer. More than 90% of the soft electrons'' ([ital E][sub [ital e]][approx lt]50 eV) are ejected in the forward direction in agreement with classical-trajectory Monte Carlo predictions. The electron longitudinal momentum is not balanced by the longitudinal momentum change of the projectile but mainly by the backwards recoiling He[sup 1+] ion. Energy losses of the 0.2 GeV projectiles as small as [Delta][ital E][sub [ital P]]/[ital E][sub [ital P]]=3.4[times]10[sup [minus]7] are observable.