2-CENTER EFFECTS IN ELECTRON-EMISSION FROM THE IMPACT OF FAST MULTIPLY CHARGED PROJECTILES ON HELIUM

The double differential cross sections (DDCS) for ejection of electrons from helium by p+, He2+, C6+and O8+of 1 MeV amu−1energy have been measured as a function of electron energy and emission angle. The DDCS show deviations from the square of the projectile-charge dependence predicted by the first Born approximation, and the deviations are seen to increase with projectile charge. The data are in agreement with calculations using a continuum-distorted-wave eikonal-initial-state model, describing the simultaneous effect of the projectile and residual target fields. This indicates that two-centre effects are important in the electron emission. © 1990 IOP Publishing Ltd.