CXVI. The interpretation of X-ray absorption spectra of solids

Abstract

Abstract A discussion is given of some recent experimental results on the fine structure of the X-ray absorption edges of solids. Recent work has shown the existence for many solids of a pronounced maximum (raie blanche) at the absorption edge. For K-absorption this may be due to one of two causes: (i) a high density of normally unoccupied states, with p symmetryin the neighbourhood of the absorbing atom; this is for example the case for nickel in oxides; and (ii) the formation of exciton levels. Exciton levels are defined as energy levels which are not formed until the electron is removed from the X-ray level, and are caused by the field round the point where the charge is missing. They are to be expected in insulators but not in metals. The experimental evidence is discussed in the light of this theoretical model, with special reference to the semi-metals gallium and arsenic.