High-resolution laser fluorescence spectroscopy, using a single-mode dye laser acting on a collimated atomic beam, has been performed to determine the hyperfine-structure (hfs) constants in six states of the 6p 5d configuration of 135Ba and 137Ba. Isotope shifts (IS) for eleven transitions between the 6s 5d and the 6p 5d configurations have also been measured. From an analysis of the energy levels, intermediate angular wavefunctions have been deduced. The wavefunctions are used to evaluate experimental hyperfine parameters from the experimental hfs constants. The parameters are, for the magnetic-dipole interaction compared with theoretical values, and for the electricquadrupole interaction used to estimate the nuclear quadrupole moments for the odd isotopes. The IS in the measured transitions are analysed using a King-plot, with the first resonance line in Ba II as the reference. Specific mass and field shifts are evaluated for the measured transitions. The field shifts have been used to determine the change in mean-square radius between the natural abundant Ba-isotopes.

Measurements of the hyperfine structures in the 6p5dlD2, 3D 1 and 3F2,3, ~ states of 135Ba and 137Ba, and isotope-shifts in several far-red transitions between the 6s 5d and 6p 5d configurations, as well as the transition 6s 2 1So-,6s6 p 3p~ at 7,911 A. have been performed using high-resolution laser spectroscopy on a collimated atomic beam of natural barium. An analysis of the magnetic-dipole interaction in the 6p 5d configuration using effective one-and two-body hyperfine operators is presented. In particular the contact interaction was studied with respect to the correlation between the two valence electrons. Effects of strong configuration interaction were found. From a King-plot analysis of the isotope shift term-and J-dependence of the field shift have been evaluated for the transitions between the 6s5d and 6p5d configurations.Relativistic Hartree-Fock (RHF) calculations have been performed of electron densities at the nucleus for six different configurations in Ba I and Ba II. The RHF calculations reproduce the experimental King-plot slopes quite well, while the absolute values, of the changes in electron density at the nucleus for the studied transitions, are found to be 9 % lower than the results derived from a muonic experiment.

Precision hyperfine structure (hfs) measurements in the 5s4d 1D 2 metastable state of STSr were performed using the laser radio-frequency double resonance method. The magnetic dipole and electric quadrupole interaction constants were found to be a= -5.5734(4) MHz and b = 55.421(6) MHz. In addition high-resolution laser spectroscopy experiments were performed in the 5s4d ~D2 ~--~ 5s6 p 1p~ and 5s4d IDz +-+ 5p4d aD z transitions in SrI. The isotope shifts in the transitions and the hfs in the upper states were determined. Comparison of the experimental results with corresponding relativistic selfconsistent-field (SCF) calculations shows that the states involved are very strongly perturbed. Therefore no reliable nuclear quadrupole moment for STSr can be deduced from the data presented here without more detailed calculations. A relativistic SCF calculation of the electron density at the nucleus was used in combination with muonic values of the nuclear mean square radii to evaluate the field shifts. From the experimental isotope shifts the specific mass shifts in the two transitions can then be deduced. This shift was found to be particularly large in the transition 5s4d aDz+-*5s6 p 1P 1 .

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