Electron-impact ionization of W5+

Electron-impact single-ionization cross sections for the W5+ ion have been studied experimentally and theoretically. Measurements of a detailed ionization spectrum and of absolute cross sections were performed employing the crossed-beams method in the energy range from the ionization onset up to 1000 eV. The experimental data show a prominent contribution of W5+ ions in metastable states. The theoretical analysis includes level-to-level calculations from the 4f(14)5s(2)5p(6)5d ground configuration and long-lived levels of the 6s, 5p(5)5d(2), 4f(13)5d(2), and 4f(13)5d 6s configurations. Direct-ionization and excitation-autoionization contributions to the total single-ionization cross sections were calculated employing a distorted-wave approximation. Radiative damping was taken into account. It is shown that correlation effects play an important role and lead to substantial reduction of cross sections. Theory and experiment are in quite good agreement when, within a statistical model, a (85 +/- 9)% fraction of parent ions in the ground configuration is assumed. The strongest contributions of metastable parent ions arise from the 5p(5)5d(2) and 4f(13)5d(2) configurations.