Electron-hole interaction in the d -electron excitations of GeS and SnS

The excitation energy of the Ge $3d$ and Sn $4d$ electrons in GeS and SnS is consistently 0.7 to 1.7 eV lower than one would expect from a combination of photoemission binding energies and optical interband transitions connecting valence and conduction bands. This, as well as the reversal of the intensity ratio of d5/2 and d3/2 excitations, is an indication for non-negligible d-hole conduction-electron interactions.