Coherent excitation in few-electron atomic collisions systems

The authors review recent advances in the coherent excitation during atomic collisions. Special attention is paid to alignment and orientation of the excited charge cloud and to the collision-induced dipole moment. The authors focus their discussion on one- and two-electron collision complexes like H + -H and (H-He) + which provide the benchmark systems for such studies. The theoretical concepts to describe the excitation process utilize the quasi-molecular picture at small velocities and use coupled-channel techniques at medium velocities; they are supplemented by intuitive models to interpret the investigated coherence parameters.