High-resolutionKLLAuger spectra of multiply ionized oxygen projectiles studied by zero-degree electron spectroscopy

High-resolution measurements of oxygen K Auger electrons have been performed using multiply charged 10-MeV ${\mathrm{O}}^{\mathrm{n}+}$ (n=2, 3, and 4) projectiles in collisions with He. Line-broadening effects are strongly reduced so that high-resolution spectroscopy is possible for Auger electrons ejected from fast projectiles. The spectra obtained for ${\mathrm{O}}^{4+}$ and ${\mathrm{O}}^{3+}$ impact show relatively simple structures dominated by lines arising from three-electron (Li-like) and four-electron (Be-like) states, respectively. Using configuration-interaction wave functions, the relativistic energies and fine structures of Li-like states are studied. The relativistic correction, Breit-Pauli operator, and mass-polarization effect are calculated for numerous resonances and metastable autoionizing states in O v i. Excellent agreement with experimental data is obtained. For example, the calculated transition energy of the (1s2s2p${)}^4$P° state is 416.02 eV. It is to be compared with the corresponding experimental data of 416.0±0.2 eV.