X-Ray Photoelectron Spectroscopy of Various Core Levels of Lanthanide Ions: The Roles of Monopole Excitation and Electrostatic Coupling

We have studied the $4d$ levels of the lanthanide ions in a number of their compounds. The $4d$ levels of the lighter lanthanides lack the satellites which appear on the $3d$ levels. This result is not unexpected if the satellites are due to shakeup of a valence-band electron to a $4f$ level as proposed previously. Limited data on the other levels having $n=3\mathrm{}$ and $n=4\mathrm{}$ are also consistent with this mechanism. We find the $4d$ levels to be affected strongly by electrostatic coupling to the unfilled $4f$ shell. Comparison of experimental spectra with predicted spectra of ${\mathrm{Ce}}^{+3\mathrm{}}$ and ${\mathrm{Yb}}^{+3\mathrm{}}$ reveals good agreement for ${\mathrm{Yb}}^{+3\mathrm{}}$ and fair agreement for ${\mathrm{Ce}}^{+3\mathrm{}}$. Possible reasons for the disagreement between the observed and calculated spectrum for ${\mathrm{Ce}}^{+3\mathrm{}}$ are discussed.