2ND-ORDER MAGNETIC CONTRIBUTIONS TO THE HYPERFINE SPLITTING OF THE 5SND(1)D(2) STATES IN SR-87

The hyperfine structure of 5snd 1D2 states in Sr-87 was studied for pr incipal quantum numbers 11 less-than-or-equal-to n less-than-or-equal- to 25 by Doppler-free two-photon excitation combined with thermionic d etection. Based on the more accurate data, compared to previous result s, the hyperfine structure was analyzed by second-order perturbation t heory using multichannel quantum-defect theory wave functions. As a re sult we find that the surprisingly large B factors obtained by fitting the data with the Casimir formula do not reflect a quadrupolar intera ction 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 demon strates 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.