For pt. I see abstract A4887 of 1969. Elastic and inelastic differential cross sections have been measured in relative values of asymmetrical rare-gas-ion-rare-gas-atom systems, in the energy range 500 eV and in the angular range 0.5 degrees -13 degrees (in the laboratory frame). The systems under investigation are: He⁺ on other rare gas atoms and Ne⁺ on He. Three types of collisions processes are considered, elastic, excitation on discrete states and excitation of the atom in autoionizing levels. The He⁺-Ne system is discussed in detail and compared to the inverse system Ne⁺-He. The excitation processes are dominated by the crossings of the non- adiabatic potential curves. The locations of the crossings have been determined for the He⁺-Ne system and for the Ne⁺-He system. At large values of tau , transitions toward several inelastic channels are to be considered; a rough calculation of the inelastic cross section is given in the case of an almost continuous series of crossings. The reduced differential cross sections for the excitations of the atom on autoionizing levels present generally a maximum at a value of tau independent of energy.