Revised energy levels and hyperfine structure constants of Nb II

Using wave number calibrated Fourier transform spectra, ranging from the IR to the UV regions, we determined with high accuracy the energies of the levels of the first ion of Niobium. In order to increase the accuracy of the center of gravity wave numbers of the observed spectral lines, the hyperfine structure was taken into account. For this purpose, the magnetic dipole hyperfine constants $A$ were determined for all involved levels. All but one of the previously known levels were included in the calculation. This level (at 91 493 cm⁻¹) is considered to be non-existent. From the experimental center of gravity wave numbers of 1121 lines we deduced the energy values of 184 levels of even parity and 164 levels of odd parity in a global fit. A comparison between our results and all previously available literature values is provided.