The hyperfine structure of the atomic levels 5d 3 6s 2 4/77/2, 9/2 and 4P1/2 in 181Ta has been studied by atomic-beam magnetic-resonance. Using intermediate coupling wave functions derived for the configurations (5d+6s) 5 the hyperfine structure data of six low-lying metastable states have been analyzed with respect to the effective operator formalism. The effective radial parameters for the magnetic dipole and electric quadrupole interactions are determined from these measurements and compared with relativistic calculations. The value obtained for the spectroscopic quadrupole moment of the l SlTa nuclear ground state is Qhfs=3.44(17)barn (uncorrected for configuration interaction effects).

Fourteen transitions in ReI, starting from high-lying metastable states belonging to the configurations (5d+6s) 7, have been studied by laser-induced fluorescence in a collimated atomic beam, and accurate values for the isotope shifts in these transitions as well as for the hyperfine structure constants of 13 metastable and 9 excited states have been obtained. In addition, high precision measurements of the hyperfine structure of the states 5d 56S 2 ~DT/2 and 5d66s 6D1/2,3/2,5/2,9/2 have been performed using the atomic beam magnetic resonance technique coupled with laser-induced state-selective detection of metastable atoms. The analysis of the hyperfine structure data yields experimental evidence for far configuration mixing effects on the off-diagonal spin-dipole matrix elements. The phenomenological interpretation of the isotope shifts shows the significance of off-diagonal field-shift effects.

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