Abstract
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 byMuller, 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.
Published Version
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