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

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.