Soft-x-ray appearance potential spectra of La and Ce from 0 to 1400 eV

The soft-x-ray appearance potential spectra were measured for La and Ce in the 0-1400-eV range. The $3d$ and $4d$ spectra exhibited prominent structure, which is discussed along with x-ray absorption and emission data. The excited electron and the core hole interact strongly, and there is evidence for additional interaction with the projectile electron. The two-density-of-states model of Wendin seems promising for explaining the spectra, but it must be extended to allow for the interaction of the projectile electron with the excited atom. The effects of oxidation are described.