K-shell excitation studied for H- and He-like bismuth ions in collisions with low-Z target atoms

The formation of excited projectile states via Coulomb excitation is investigated for hydrogenlike and heliumlike bismuth projectiles (Z = 83) in relativistic ion-atom collisions; The excitation process was unambiguously identified by observing the radiative decay of the excited levels to the vacant Is shell in coincidence with ions that did not undergo charge exchange in the reaction target. In particular, owing to the large fine-structure splitting of Bi, the excitation cross sections to the various L-shell sublevels are determined separately. The results are compared with detailed relativistic calculations, showing that both the relativistic character of the bound-state wave functions and the magnetic interaction are of considerable importance for the K-shell excitation process in high-Z ions such as Bi, The experimental data confirm the result of the complete relativistic calculations, namely, that the magnetic part of the Lienard-Wiechert interaction leads to a significant reduction of the K-shell excitation cross section. [S1050-2947(98)00801-4].