The chemical shift dI of the ionization energy I of the inner shells is not only dependent on the oxidation state of a given element, but also on the ligands. Even for a fixed oxidation state, dI has been shown to vary between 2 and 8 eV in a comparative study of all elements which are neither noble gases nor strongly radioactive. However, this conclusion is, to some extent, modified by reproducible positive potentials on non-conducting samples which have been measured between 1 and 4V in typical cases and compared with the theory for almost ionic cubic crystals and with experiments with mixtures of non-conducting powdered MgF₂, BaS0₄ and ThF₄ and metals such as Au, Tl₂O₃ and CuS. The widths and highly varying intensities of photo-electron signals are theoretically discussed. The d and f shells of transition and post-transition group atoms give relatively intense signals even for I between 8 and 30 eV since the 1486.6 eV photons most readily ionize shells with small average radii. Interesting relations can be established with electron transfer spectra and optical electronegativities.

The effects of interelectronic repulsion produce multiple signals when the groundstate has positive S. Special satellites occur in copper(II), lanthanum(III) and other lanthanide compounds. A systematic study is made of alkaline metal, tetra-alkylammonium, tetraphenylarsonium, methylene blue and Co en₂Cl₂⁺ salts of several anions. The adaptation of the electronic density of the neighbour atoms in the ionized system contribute to dI which cannot be explained exclusively on the basis of fractional atomic charges and the Madelung potential.