Resonant photoemission in transition-metal chlorides

In the chlorides of Ni, Co, Fe, and Mn, the resonance between the excitations of valence electrons and the $3p$ electrons of the metal ions is observed over the whole parts of the valence-band spectra including ligand-derived bands as well as satellites. The trend of the systematic change in satellite—to—main-band separations in going from Ni${\mathrm{Cl}}_2$ to Mn${\mathrm{Cl}}_2$ is opposite to that in the energies of charge-transfer excitons, and this is discussed in connection with the electron-shakedown mechanism of the hole-induced covalency. Excitation spectra consist of two or three overlapping bands approximately with Fano line shapes. The $q$ value characterizing a Fano line shape is larger for satellites and ligand-derived bands than for the $3d$ bands of the metal ions. The resonant enhancements of the ionization cross sections of the main bands increase from Ni${\mathrm{Cl}}_2$ to Mn${\mathrm{Cl}}_2$. These aspects are interpreted in terms of the hybridization of the $3d$ orbitals of the metal ions and the $3p$ orbitals of the ligand ion. The ordinary $M_{2,3}\mathrm{VV}$ super-Coster-Kronig bands are very weak.