Evidence of Effective Potential Barriers in the X-Ray Absorption Spectra of Molecules

Abstract

We interpret the enhanced lines and frequent failure to detect Rydberg structure in the x-ray absorption spectra of molecules in terms of ``inner-well'' and ``outer-well'' states which result from an effective potential barrier located near the electronegative atoms in the molecule. The K and LII, III spectra of sulfur in SF6 are discussed in detail and all prominent features are identified. X-ray absorption spectra of molecules in which a B, S, or Si atom is combined with two or more electronegative atoms are surveyed to illustrate further the influence of effective potential barriers. It is pointed out that ``inner-well'' states have been observed in emission experiments, and that such states should also be observed in electron scattering experiments on molecules and in x-ray absorption experiments on ionic crystals. Finally, cases are described in which x-ray absorption measurements may permit the determination of the geometry of molecules.