Saddle-point effects in adiabatic to intermediate-energy ion-atom collisions

An overview will be given of the many experimental and theoretical studies of saddle-point phenomena, with special emphasis on adiabatic collisions and simple systems. For such cases, experimental evidence for the actual existence of saddle-point electrons has been obtained by different groups using different techniques. At intermediate-energy collisions, the observation of saddle-point effects is still a controversial issue. It will be argued that even though for these relatively fast collisions the underlying saddle-point mechanism may still be present, no pronounced saddle-point features should be expected. (orig.)