Hyperfine-structure studies of Nb II: Experimental and relativistic configuration-interaction results.

Abstract

We report an experimental and theoretical study of the hyperfine structure (hfs) in various metastable states in $^{93}\mathrm{Nb}$ ii. Hyperfine structures of five levels in Nb ii have been measured using a combination of the laser-rf double resonance and laser-induced fluorescence methods in a collinear laser--ion-beam geometry. Theoretically, for J=2, a multireference calculation of energies and hfs based on a relativistic configuration-interaction methodology of the lowest ten levels in the (4d+5s${)}^{4}$ manifold is reported. The average energy error is 450 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Many of the hyperfine constants show large changes from the Dirac-Fock values and the magnetic dipole constant has a 4% accuracy for the one J=2 level measured. We have also identified all the core-valence and core-core effects that dominate the energy differences and hfs.