In the analysis of high-resolution Doppler-free two-photon hyperfine-structure (hfs) measurements of levels in the Eu i term ${}_{}{}^6{}_{}{}^{}\mathrm{D}$ of the configuration 4${\mathit{f}}^7$6s6d of ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ and ${}_{}{}^{153}{}_{}{}^{}\mathrm{Eu}$ the necessity occurs to take into account also hfs perturbations. For the magnetic hfs interactions of ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$, the following off-diagonal matrix elements ${}_{}{}^{151}{}_{}{}^{}$${\mathit{A}}_1$(JJ’) could be determined from the high-resolved two-photon line profiles: ${}_{}{}^{151}{}_{}{}^{}$${\mathit{A}}_1$(1/2,3/2)=5.70(3) GHz, ${}_{}{}^{151}{}_{}{}^{}$${\mathit{A}}_1$(3/2,5/2)=4.3(2) GHz, ${}_{}{}^{151}{}_{}{}^{}$${\mathit{A}}_1$(5/2,7/2)=2.9(2) GHz, ${}_{}{}^{151}{}_{}{}^{}$${\mathit{A}}_1$(7/2,9/2)=2.2(2) GHz. The high quality of the calculations is represented both in the reproducibility of the absolute hfs level energies and also in the hfs anomaly where a mean value deduced from the corrected magnetic hfs constants of -0.66(8)% can be stated.

• Received 1 April 1991

DOI:https://doi.org/10.1103/PhysRevA.44.5737