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

抄録

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 L₃ 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.