Soft X-Ray Absorption Spectra of Alkali Halides. I. KCl and NaCl

Abstract

Soft X-ray absorption spectra of typical alkali chlorides, KCl and NaCl, were observed by using as a continuous background the synchrotron radiation from the 750 MeV electron synchrotron in the Institute for Nuclear Study, Tokyo. The L 2,3 -absorption spectrum of Cl - in these chlorides has been obtained. The spectrum shows one or two sharp absorption maxima at the long wavelength limit and a rapid increase in absorption at about 9 eV above the limit. A shoulder-like structure is observed at the foot of the second absorption band. A tentative X-ray energy level diagram suggests that the shoulder corresponds to the onset of interband transition from L 3 to the conduction band. The first absorption maximum is accordingly interpreted as the excitation of a stable X-ray exciton; a metastable X-ray exciton seems to be involved in the second maximum. The spectral behavior of the L 2,3 -absorption near the long wavelength limit has some similarity to the optical absorption spectrum in the vacuum ultraviolet region. It is suggested that the sharp rise in absorption at about 9 eV above the limit is due to two electron excitation by a single photon.