Electronic Core Levels of theIIB−VIACompounds

X-ray induced electron-emission measurements were used to determine the energy levels of core electrons in ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgS, HgSe, and HgTe. The investigated energy range extends from the bottom of the valence band to about 1200 eV below the Fermi level. Chemical shifts were determined by comparing our results with experimental values for the pure elements. These shifts are plotted as a function of the fractional ionicity values determined by Phillips and Van Vechten, Pauling, and Coulson. Spinorbit-splitting values were experimentally determined for the first time for several levels including the $\mathrm{Zn}3d$, $\mathrm{Cd}4d$, and $\mathrm{Hg}5d$ levels. Furthermore, our measured energy values for these levels are used to determine the absolute energy values of the initial and final states of transitions normally labeled $d_2$ in ultraviolet reflectivity and electron-energy-loss measurements. Our results for ZnSe and CdTe are compared with self-consistent relativistic orthogonalized-plane-wave calculations for the excitation energies of these compounds. Agreement with these theoretical calculations is best for the levels closest to the valence band and appears to be angular momentum dependent.