Photoemission and Valence Band Structure of Alkali Iodides

Energy distributions are described for external photoelectrons ejected from CsI by photons of energy 11.3 ev. All but about 5% of the photoelectrons emerge with kinetic energies between 1.5 ev and 5.3 ev. The conspicuous lack of electrons at lower energies is interpreted in terms of a valence band of width about 3 or 4 ev with an upper edge lying about 6 ev below the vacuum level. Related results are mentioned for RbI, KI, NaI, CsBr, and CsCl.