2-CENTER ELECTRON-ELECTRON INTERACTIONS IN COLLISIONS OF FAST NE7-IONAND NE6+-ION WITH GAS ATOMS()

Experimental and theoretical studies of the two-center electron-electr on interaction occurring during energetic ion-atom collisions are pres ented. Experiments were performed using the accelerator facility VICKS I at HMI, Berlin. Electron spectra from Auger and Coster-Kronig transi tions following the excitation of a highly charged neon projectile hav e been studied by zero-degree electron spectroscopy, Various target at oms with atomic numbers ranging from 1-18 were used as exciting partne rs. We applied both impact parameter treatments and the plane wave Bor n approximation to describe screening effects and dielectronic two-cen ter processes (''antiscreening''). We found that the 1s-2l excitation of the Ne7+ projectile at 8.5 MeV/u impact energy is mainly due to the screened target nucleus. In contrary? two-center processes are likely to be dominant in the 2s-nl excitation of the 6 MeV/u Ne6+ projectile . The 2s-nl cross sections are roughly proportional to the number of e lectrons per target atom. This fact suggests that, in disagreement wit h first order theories? the 2s-nl excitation is significantly governed by the two center electron-electron interaction.