Time-of-flight study of medium energy range collisions of metastable helium atoms with atomic or diatomic molecular targets

Collisions of He(23S) on atomic (He, Ar) or molecular (D2,02) targets are experimentally investigated at low keV energies (0.1-1.5keV) by a time-of-flight technique. The method yields an overall picture of the various inelastic processes and their relative probabilities. Direct experimental evidence of the importance of the He(23P) and He(n'l') n'>=3 excitations of the projectile with He and D2 targets is reported. With an 02 target differential cross sections for He+ production measured at various energies reveal a rainbow feature. With the Ar target, the predominance of Penning ionisation and excitation transfer processes is confirmed. The experimental results concerning the He*-He system have been compared with the predictions of available theoretical models. (author)