Many-electron phenomena in the ionization of ions

This brief review of many-electron phenomena in the single and multiple ionization of ions tries to elucidate connections between ion-atom collisions and interactions of single free electrons and photons with neutral or charged atomic species. With the capability of using multiply charged ions in collisions with charged particles or photons, conventional studies on neutral targets can be extended to a new dimension: the target charge state. This is especially interesting for studies of selected effects along specific isoelectronic sequences, i.e. of n-electron atoms with variable nuclear charge. The necessary colliding-beams and merged-beams techniques are technically demanding but can provide access, for example, to electron correlation effects in collisions under the influence of increasingly strong electron-nucleus interactions.