J off-diagonal effects in the hyperfine-structure splitting in the Eu I term e6D of 4f76s6d

In the analysis of high-resolution Doppler-free two-photon hyperfine-structure (hfs) measurements of levels in the Eu I term 6D of the configuration 4f76s6d of 151Eu and 153Eu the necessity occurs to take into account also hfs perturbations. For the magnetic hfs interactions of 151Eu, the following off-diagonal matrix elements 151A1(JJ') could be determined from the high-resolved two-photon line profiles: 151A1(1/2,3/2)=5.70(3) GHz, 151A1(3/2,5/2)=4.3(2) GHz, 151A1(5/2,7/2)=2.9(2) GHz, 151A1(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