Resonant photoemission in CeS and CeP

Direct and resonant photoemission experiments on CeS and CeP show that the $4f$ level lies in a band gap in CeS but overlaps the valence band in CeP. At the $4d\ensuremath{\rightarrow}4f$ resonance threshold the $4f$ level and the valence-band emission features are found to be weakly coupled in CeS and strongly coupled in CeP.