Charge state effect on the K-shell ionization of iron by xenon ions near the Bohr velocity

Fe K-shell ionization cross sections induced by 2.4-6.0 MeV Xe ²⁰+ are measured and compared with different binary-encounter- approximation (BEA) models. The results indicate that the BEA model corrected both by the Coulomb repulsion and by the effective nuclear charge (Z _eff) agrees well with the experimental data. Comparison of Fe K-shell X-ray emission induced by 5 MeV xenon ions with different initial charge states (20+, 22+, 26+, 30+) verifies the applicability of the effective nuclear charge (Z_eff) correction for the BEA model. It is found that Z _eff correction is reasonable to describe direct ionization induced by xenon ions with no initial M-shell vacancies. However, when the M shell is opened, the Z_eff corrected BEA model is unable to explain the inner-shell ionization, and the electron transfer by molecular-orbital promotion should be considered.