Experimental and semi-empirical studies of the fine and the hyperfine structure of odd-parity configuration system of atomic lutetium

In this paper, we present the results of the fine- (fs) and the hyperfine structure (hfs) analysis of atomic lutetium (Lu I). In the experimental part of this work, 24 magnetic-dipole (A) and 20 electric-quadrupole (B) hfs constants were measured for odd-parity configuration levels, together with 5 A and 5 B hfs constants for even-parity configuration levels, using laser spectroscopy in a hollow cathode discharge lamp or calculated from the Fourier transform spectrum. Based on these results, as well as on available literature data, a parametric study of the fs and hfs was performed for the system of 84 odd-parity configurations of atomic lutetium. The fs fit for 128 energy level values resulted in a mean error of $\Delta E=14$ cm⁻¹. For unknown electronic levels, predicted values of the level energies and the hfs constants are given. These predictions, along with the significant improvement in the accuracy of the experimental databases, lay the foundation for the next step of the Lu I radiative transition probabilities analysis.