Hyperfine structure of excited 4f115d6s2levels inErI167: Measurements and multiconfiguration Dirac-Fock calculations

The laser-rf double-resonance technique has been used to make precise measurements of the hyperfine structure (hfs) of 10 excited 4$f^{11}$5d6$s^2$ levels in ${}_{}{}^{167}{}_{}{}^{}\mathrm{Er}$. The results are compared with multiconfiguration Dirac-Fock calculations using the known nuclear moment values. For the dipole hfs, agreement with experiment is reasonably good. For the quadrupole hfs, agreement is relatively good if allowance is made for different shielding in the 4f and 5d shells. The theory is less successful where the 4f and 5d contributions tend to cancel. Sternheimer factors $R_{\mathrm{nl}}$ are obtained. Precise hfs studies are also made for one highly excited 4$f^{12}$6s6p level. Less precise results are given for hfs of more highly excited levels and for isotope shifts of a number of optical lines.