Bestimmung der Kernquadrupolmomente der beiden stabilen Europiumisotope aus dem Eu II-Spektrum

The hyperfine structure of the transitions 4f ⁷ 6p ⁹ P _3,4,5?4f ⁷ 6s ⁹ S ₄,⁷ S ₃ in the spark spectrum of europium was investigated by a digital recording double-Fabry-Perot-spectrometer. Enriched samples of¹⁵¹Eu and¹⁵³Eu were used in hollow cathode light sources cooled in liquid air. As the hyperfine splitting of the⁹ P levels was not completely resolved the patterns were analysed by a computer. TheA- andB-values of the⁹ P levels were determined for both isotopes. Together with the experimentalA-values of the⁷ P levels theseA-values were used to check the eigenfunctions ofBordarier, Judd, andKlapisch, which have been calculated for intermediate coupling. Good agreement between observed and calculatedA-values was reached only if the spherical-symmetric part of the magnetic hyperfine interaction operator of the 6p-electron was used as a free parameter. In this way the configuration interaction between 4f ⁷ 6p and 4f ⁶ 6s 6d can be taken into account. Fortunately this mixing does not affect the quadrupole interaction. Therefore the quadrupole moments were derived from the measuredB-values using the unperturbed eigenfunctions. The resultsQ(¹⁵¹Eu)=(1.12 ±0.07) · 10^?24 cm² andQ(¹⁵³Eu)=(2.85 ± 0.18) · 10^?24cm² are in complete agreement with the values obtained byMüller, Steudel, andWalther in the 4f⁷ 6s 6p levels of the arc spectrum of europium. The values found for the hyperfine anomaly agree very well with the values derived from levels in Eu I and Eu III.