Laser-rf double-resonance measurements of the hyperfine structure in Sc ii

The hyperfine structure of all levels of the metastable 3$d^2$ configuration in Sc i i has been measured with high precision by collinear fast-ion laser-rf double-resonance spectroscopy. The double-resonance technique improved the precision of the earlier results by more than a factor of 150. The enhanced precision made possible for the first time a meaningful comparison between experimental and multiconfiguration Dirac-Fock calculated B values. The comparison showed that, unlike the A values where disagreements between experiment and theory could be greater than 400%, the B values were well predicted.