The hyperfine structure of 5snd ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ states in ${}_{}{}^{87}{}_{}{}^{}\mathrm{Sr}$ was studied for principal quantum numbers 11≤n≤25 by Doppler-free two-photon excitation combined with thermionic detection. Based on the more accurate data, compared to previous results, the hyperfine structure was analyzed by second-order perturbation theory using multichannel quantum-defect theory wave functions. As a result we find that the surprisingly large B factors obtained by fitting the data with the Casimir formula do not reflect a quadrupolar interaction but rather consist predominantly of second-order magnetic dipole contributions. Further, inconsistencies in the King plot of odd-even isotope shifts were removed by this type of analysis. The result demonstrates the importance of higher-order effects in hyperfine splittings of excited states in atoms with two valence electrons, even when the fine-structure splitting is large compared to the hyperfine splitting.

• Received 20 January 1993

DOI:https://doi.org/10.1103/PhysRevA.47.4725