Density of valence states of CuCl, CuBr, CuI, and AgI

Abstract

The photoelectron energy distribution curves for CuCl, CuBr, CuI, and AgI have been measured for $\hslash \omega =16.8, 21.2, 26.9, 40.8, 48.4, \mathrm{and} 1486.6$ eV. By exploiting the strong dependence on $\hslash \omega$ of the photoionization cross sections of the atomic levels comprising the valence band, we have been able to determine the $s$, $p$, and $d$ partial densities of valence states. These results compare well with those obtained by x-ray fluorescence and x-ray photoemission, but have better resolution. It is found that the $d$ levels of ${\Gamma }_{12}$ symmetry remain corelike, while the ${\Gamma }_{15}$ $d$ levels band significantly. In the Cu compounds the ${\Gamma }_{15}$ levels of predominantly $d$ character lie above the ${\Gamma }_{12}$ bands, which in turn lie above the mainly $p$-like ${\Gamma }_{15}$ levels. This level ordering is reversed in AgI. The band structure and densities of valence states computed from a seven-function basis set, consisting of four bonding $s-p$ orbitals and three $d_{\mathrm{xy}}$ orbitals, are shown to reproduce the trends observed in the density of valence states of these compounds.