Interpretation of the structures observed for excitation cross-sections inC2+/He2+-Li collisions

The existence of oscillatory or plateau like structures in the low energy d ependence of the excitation cross-sections in ion-atom collisions has recen tly been subject of different interpretations based on model calculations. We report atomic-state close-coupling calculations for the description of L i(2s --> 2p) excitation by He2+ and C2+ impact where the appearance of such structures is very different and previously documented in experimental stu dies. A system specific interpretation based on dynamic adiabatic energy cu rves is given and the interplay between high-energy direct and low-energy m olecular mechanisms in the two systems are discussed.