Two- and three-body effects in single ionization of Li by 95-MeV/u Ar18+ projectiles: Analogies with photoionization

Cross sections for single electron emission have been measured in collision s of 95-MeV/u Ar18+ projectiles with atomic Li for electron energies rangin g from 3 to 1000 eV and angles ranging from 25 degrees to 155 degrees. Mode ls based on the Born approximation are introduced to separate two- and thre e-body effects in the angular distributions of the ejected electrons. Both experiment and theory provide information about the separability of the two - and three-body effects. The high projectile velocity and the use of the L i target are shown to be essential for the present analysis. The emission o f the is electron is attributed mainly to three-body effects. The cross sec tion for three-body collisions rapidly decreases with the electronic energy transfer involving a power law with an exponent of -3.5. Consequently, two -body effects dominate at high electron emission energies. Remarkably large contributions from two-body collisions were also observed for the low-ener gy emission of the 2s electrons. Demonstrating the: analogy in ionization b y photons and ions, the two- and three-body processes are associated with C ompton scattering and photoabsorbtion, respectively. [S1050-2947(99)05202-6 ].