New Interpretation of the Soft-X-Ray Absorption Spectra of Several Alkali Halides

Abstract
Theoretical calculations have thus far been used to interpret the soft-x-ray spectra of several alkali halides in terms of band structures alone, excluding the possibility that core excitons are formed below the band edge. By independently determining the threshold for band transitions from x-ray photoemission spectroscopy and optical-gap data, we conclude that these spectra are in fact almost entirely excitonic in nature.