Hyperfine structure of Sc ii: Experiment and theory

Collinear laser–ion-beam spectroscopy has been used to measure hyperfine structure (hfs) in three levels of the 3$d^2$ and six levels of the 3d4p configuration of Sc i i. The results combine with earlier measurements of hfs within these configurations to give a fairly complete picture of hfs in these configurations. The combined results are compared with multiconfiguration Dirac-Fock (MCDF) ab initio calculations. Good agreement is obtained for the magnetic dipole hfs constants of the singlet states in both the 3$d^2$ and 3d4p configurations, but the MCDF predictions for the triplet states are not even qualitatively correct. The poor agreement for the triplet states appears to be due to the neglect of core polarization in the present MCDF approach.