X-ray photoelectron spectra of ZrS3 and ZrSe3 have been recorded. These compounds may be regarded as Zr(Ch2)Ch (Ch=S,Se) with both (Ch2) groups and isolated Ch atoms. An unambiguous assignment of the chalcogen core levels was made by comparing the spectra with those of ZrS2 and ZrSe2 (where all chalcogen atoms are isolated). The levels of the (Ch2) groups are found at higher binding energies than those of the isolated Ch atoms, which is consistent with a larger negative charge on the isolated atoms. The structures of the valence bands of ZrS3 and ZrSe3 are discussed in terms of a molecular-orbital scheme for the (Ch2) groups. The exciton peaks observed in the optical absorption spectra of ZrS3 and ZrSe3 are assigned as due to excitations of the (Ch2) groups. © 1974.