We have investigated the collisional excitation of hydrogen atoms by protons and multiply charged ions at intermediate velocities applying the optical method. The population or the np levels (n = 2,. . . ,6) has been determined for a variety of projectiles with charge states q ranging from I + to I I + and scaled velocities U/& between 0.7 and 5.6au. The cross &ions are shown to fulfil the scaling relation o / q = f ( d / q ) with respect to the projectile charge q and velocity U for q>3. The relevan= of scaled intermediate velocities for a classification o f excitation mechanism is pointed out.

The authors have investigated the collisional excitation of He by protons and multiply charged ions at intermediate velocities applying the optical method. The population of the magnetic sublevels of He 41D has been determined using level-crossing techniques for a variety of projectiles with charges ranging from 1+ to 23+ and velocities between 1 au and 7 au. The relative excitation cross sections sigma M/ sigma 41D of the Zeeman substates turn out to be universal functions UM( nu 2/q) of the projectile velocity nu and charge q. Total excitation cross sections of the 31P, 41S and the 41D state are included for a discussion of the scaling relation sigma /q=f( nu 2/q).

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Total cross sections for the production of He+(2p) in collisions of H+ and e- with He at energies from 75 to 800 keV and from 0.8 to 7 keV respectively were measured. The ratio of the cross sections for He+(2p) production and for single ionization is discussed to investigate the contribution of electron correlations in the two-electron transition leading to He+(2p). For the first time the impact of H2+ and H3+ ions in comparison with H+ impact has also been studied for the energy range mentioned above.