The multiconfigurationDirac-Fock (MCDF) method is used to calculate excitation energies,Lande g values, and hyperfine-structure (hfs) constants for the lowest multiplets of the 4f 6s configurations of neutral rare-earth atoms. Although no adjustable parameters are used, the results are in rather good agreement with experiment. The calculated excitation energies and dipole hfs constants (using the known moment values) differ from experiment by typically 5%, and the g values by 0.1%. Relative to quadrupole moment values determined from muonic-atom hfs or Coulomb excitation, the calculated electric-quadrupole hfs is typically (30+2)% too large, consistent with a Sternheimer shielding factor (not included in the MCDF calculations) of R4f --+0.23. The calculated J dependence for all four observables is generally in good agreement with experiment for the ground multiplets. Particular cases where the MCDF results are less accurate are identified and discussed.

The atomic-beam laser-rf double-resonance method has been used to measure precisely the dipole and quadrupole hyperfine structure {hfs}of 11 levels of the Sd 6s configuration and four levels of the 5d configuration of ' La I. The results, together with earlier results for lower-lying levels, are compared in detail with new multicon6gurationDirac-Fock (MCDF} ab initio calculations. The agreement is good to fair overall, but is poor in some areas. The comparison yields new insights and suggests areas in which the theoretical approach must be improved. In particular, the theory underestimates the importance of contact hfs in the Sd26s con5guration by 25-409o. In addition" there is at present no self-consistent way in the MCDF approach to take account of the large core polarization observed in the 5d'4F term.

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The hyperfine structure of the seven lowest atomic levels in Co 59 has been examined with the atomicbeam magnetic-resonance technique. Quantitative agreement with earlier measurements is found for those states for which results have been published. All of the results are corrected for the effects of off-diagonal hyperfine interactions, and the effective-operator theory used for the interpretation also takes into account such effects as intermediate coupling, configuration interaction, and relativistic effects. The emphasis is on examining the consistency of the results from state to state. Although a very high degree of agreement between theory and experiment is found, some difficulty is encountered in understanding details of the quadrupole interaction. Values for the quadrupole moment of the Co 69 nuclear ground state are determined in each of two electron configurations. The difference between the two values found is well outside experimental error and is presumably due to different Sternheimer shielding in the two configurations. The value found for Q is consistent with earlier determinations and with nuclear theory. Values are given for the electronic g factor in each state examined.