Hyperfine structure of high-Lstates ini143,145by atomic-beam laser-rf double resonance

The atomic-beam laser-rf double-resonance technique has been used to study the hyperfine structure (hfs) of the metastable ${}_{}{}^7{}_{}{}^{}$ ${\mathit{L}}_{5–11}$ and ${}_{}{}^7{}_{}{}^{}$ ${\mathit{K}}_4$ states of the 4${\mathit{f}}^4$5d6s configuration in ${}_{}{}^{143,145}{}_{}{}^{}\mathrm{i}$. Four zero-field intervals were measured in each state and the results used to assign the conventional hfs constants A and B. Comparison of the results with predictions of the Sandars-Beck model allowed evaluation of the relevant single-electron radial hfs integrals. These are compared with earlier results from the Nd i atomic ground term and with extrapolations from other rare-earth elements. The unusually large orbital-angular-momentum values (L=7 and 8 for the states studied) do not appear to have introduced any anomalous effects. Ab initio calculations are not yet feasible for the complex 4${\mathit{f}}^4$5d6s levels studied.