No abstract

The saturation effect in the excitation cross sections has been investigated for Si 12ϩ ions colliding with gas target atoms ͑atomic number Z t between 2 and 54͒ in the ͑8-12͒-a.u. velocity range, both experimentally and theoretically. The experimental excitation cross sections have been deduced from the measured Ly x rays following the decay of the excited atoms. Theoretical calculations have been performed using the first Born approximation, the symmetric eikonal continuum distorted wave ͑SECDW͒ approximation, and the Schwinger variational principle ͑SVP͒. Similar to the earlier observations on the heavier ion species, the saturation has been found in both the experimental and the SVP cross sections in the entire velocity range. The SECDW approximation, however, has been found to underestimate the cross sections at large values of Z t in the presently investigated systems. In the light of these findings, the role of higher-order effects within different theoretical models has been reviewed and the possible interaction mechanisms have been discussed.

No abstract

No abstract

We have measured, for the first time, subshell-resolved L-K (L 1 -K, L 2 -K and L 3 -K) electron transfer cross sections for electron transfer from the L-shell of the target to the vacant K-shell of the projectile. These cross sections are derived by measuring the charge-state dependence of the target L x-rays from a thin Au target using bare and H-like sulphur ions. In addition, the subshell-resolved ionization cross sections are also derived from the analysis of the L x-ray production cross sections. We found that the vacancy production cross section for the L 2 subshell is much smaller than that for strongly bound L 1 subshell and the L 2 -K transfer cross section is also much smaller than the L 1 -K transfer cross section. These observations are contrary to the prediction of first-order theories.