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 $4d\to 4f$ resonance threshold the $4f$ level and the valence-band emission features are found to be weakly coupled in CeS and strongly coupled in CeP.

• Received 21 November 1980

DOI:https://doi.org/10.1103/PhysRevB.24.544