A perturbed energy level of the holmium atom

This study focuses on two lines of atomic holmium for which standard hyperfine structure analysis could not be performed. The lines were studied by laser-induced fluorescence spectroscopy using a Ti-sapphire laser. Usually, the hyperfine structure of spectral lines is described by the well-known Casimir formula. However, this was not possible in the analysis of these two lines. The common feature of these two lines is that their upper energy levels are identical. In this study, hyperfine structure analyses were performed by considering a perturbation in the hyperfine splitting of the upper energy level of both lines. Shifts were introduced for the hyperfine sub-levels with F = 4 to 7 of the perturbed level, with the help of which the positions of all components of both laser lines could be satisfactorily explained. The same behaviour was found for three other spectral lines present in the Fourier transform spectrum, which are connected to the same perturbed upper energy level. The perturbation must be caused by a hitherto unknown energy level of odd parity with small J -value. The energy, J - quantum number and hyperfine constant A of this level were estimated.