Core level excitations in the lanthanides by electron energy loss spectroscopy. I. 4d and 3d excitations

Core electron energy loss spectroscopy in reflection geometry is applied to 4d and 3d excitations in the lanthanide series La-Lu. In 4d to 4f excitation electric dipole forbidden transitions are clearly identified in the lower half of the series, while the heavy lanthanides tend to show enhancement of already dipole-allowed transitions, to states of high total angular momentum, if the exciting primary electron energy is lowered towards excitation threshold. Even stronger non-dipole effects appear for 3d to 4f transitions, but individual multiplets are not clearly resolved due to reduced d-f exchange coupling.