Laser induced fluorescence spectroscopy has been applied to measure the hyperfine structure and isotope shift of osmium I spectral lines in the visible range. Precise values for the hyperfine structure constants A and B of the most abundant odd mass isotope 189Os and the level isotope shift of altogether 43 excited energy levels were determined evaluating the measurements. Osmium in its natural abundance as well as an enriched sample of 189Os were used during the experiments. Additionally, a parametric analysis of the fine structure, the hyperfine structure and the isotope shift has been performed for the three even configurations 5d66s2, 5d76s and 5d8. Finally, the nuclear electric quadrupole moment Q for the isotope 189Os is determined to Q(5d66s2 = 0.98 (8) b for the configuration 5d66s2 and Q(5d76s = 0.97 (9) b for the configuration 5d76s.

Abstract. The Ta I line 6356.14 ~, up to now classified as the transition 5 d 36 s 2 a 4 P5/2 --5 d 36 s (a 5 F) 6 p z 4 NO/2, is a blend with a second transition, which is related to the additional levels 5d4(b3G)6s a4G9/2-39641.24 cm -1 J = 7/2 °. Using laser excitation with optogalvanic and laser-induced fluorescence detection, the hyperfine constants of the four levels involved and the distance of the center wavelengths of the two fine structure transitions could be determined.