Aims. We report on experimental studies of hyperfine structure splitting of neutral niobium. Methods. We used high-resolution Fourier transform spectroscopy to record a spectrum of niobium produced with a hollow cathode discharge lamp in the range of wavenumbers from 10 000 cm −1 to 30 000 cm −1 . Results. The magnetic dipole hyperfine structure constants A were determined for the 109 levels of odd parity by analyzing the profiles of 224 spectral lines. The A values of 57 of these level are reported for the first time.

In this work a parametric study of the fine and hyperfine structure (hfs) for the even parity configurations of atomic niobium (Nb I) is presented. A large amount of new experimental data, published during the last decade, have been considered for the fine and hfs analysis. A multi-configuration fit of 14 configurations have been performed by taking into account second-order of perturbation theory including the effects of closed shell-open shell excitations. Predicted values of level energies as well as magnetic dipole and electric quadrupole hfs constants of A and B are listed, if no experimental values are available.

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Optogalvanic laser spectroscopy has been applied to measure the hyperfine structure of 19 spectral lines of La I in the wavelength regions from 570 to 590 nm and 700 to 825 nm. Experimental hyperfine structure constants A and B of the isotope139La have been measured for 16 levels of odd parity. From those values six magnetic dipole and ten electric quadrupole constants have been determined for the first time. Some disagreements with previously obtained values are discussed.

In an experimental setup with a high-resolution Fourier transform (FT) spectrometer and a hollow-cathode discharge, bandpass interference filters are used to enhance the sensitivity. This extension leads to an improvement of the signal-to-noise ratio in the spectrum of atomic niobium by a factor of up to 10 compared to FT spectra measured previously without filters (see Kröger et al 2010 Astron. Astrophys. 516 A70). Several additional spectral lines with low intensity have been observed. Additionally, in some intense lines, blends become visible due to the better signal-to-noise ratio. The hyperfine structure of 51 lines recorded in the wavelength range from 415 to 670 nm is analysed or re-analysed and magnetic dipole hyperfine structure constants A of 8 levels of even parity and 43 levels of odd parity are determined. Improvement of sensitivity of FT spectroscopy in the visible wavelength range enabled the determination of new hyperfine structure constants A for two energy levels of even parity, which fill the last gaps for energetically low-lying levels below 14 000 cm−1. Additionally, ten new A constants for energetically higher lying levels of odd parity as well as several improved A values have been obtained.