The $K$-shell diagram ($K{\alpha }_{1,2}$ and $K{\beta }_{1,3}$) and hypersatellite (HS) $\left(K^h{\alpha }_{1,2}\right)$ spectra of Y, Zr, Mo, and Pd have been measured with high energy-resolution using photoexcitation by 90 keV synchrotron radiation. Comparison of the measured and ab initio calculated HS spectra demonstrates the importance of quantum electrodynamical (QED) effects for the HS spectra. Phenomenological fits of the measured spectra by Voigt functions yield accurate values for the shift of the HS from the diagram lines, the splitting of the HS lines, and their intensity ratio. Good agreement with theory was found for all quantities except for the intensity ratio, which is dominated by the intermediacy of the coupling of the angular momenta. The observed deviations imply that our current understanding of the variation of the coupling scheme from $LS$ to $jj$ across the periodic table may require some revision.

• Received 15 December 2008

DOI:https://doi.org/10.1103/PhysRevA.79.062512