Chemical Effects on Core-Electron Binding Energies in Iodine and Europium

Abstract

A theoretical and experimental study was made of the shift in atomic· . . ·core-electron binding energies caused by the chemical enviro~~ent.Tiw models are presented to account for these "chemical shifts." The first uses an energy cycle to break the core-electron binding energies into a free-ion contribution and a classical Madelung energy contribution. The Madelung energy contributes a significant part of the binding energy shift. It can in principle be evaluated rigorously, although there is some ambiguity as to a surface correction. The reference level for binding energies must also be considered in· comparing theory with experiment (or in comparing. experimental shifts . with one another). Electronic relaxation could also introduce errors of :V1 eV in , . .shift measurements .• The second, more approximate, model consists.of a "charged-.shell" approximation for bonding electrons in atomic complexes. It gives semiquantitative estimates of shifts and demonstrates the relationship between bond polarity and core-electron binding energy shifts.These models indicate that several features of the free-ion state will be reflected also .in chemical shifts. of a valence electron shifts the binding energies of all core levels by nearly equal amounts (10-20 eV). This shift decreases with increasing atomic nQ~ber in a given chemical family. The removal of an inner "valence" electron (e.g.) 4f in europiQ~)gives rise to relatively large shift~ ("'20 eV). These features were also found in the exper imentar .chemical shifts There are two main techniques for ~tudying the bindingenergies of atomic .., core electrons. Traditionally, x-ray emission and absorption spectroscopy have been used in this type of investigation. However, during the last ten years a photoelectr.on · spectroscopic method has been developed to sufficient precision and accuracy that it now surpasses the x-ray techniques in many respects. A detailed description of the technique has previously been published. 1 The method is simple and direct. Photoelectrons. from inner shells are expelled by x-radiation of known.energy. The kinetic energy of these photoelectrons is measured in a high resolution electron spectrometer. From the photon energy and the kinetic energy ' the binding energy of a particular subshell is readily obtained.Chemical effects on core-electron binding energies have been observed. . 2 since about 1920 in x-ray emission and more often in x-ray absorption spectra.However, experimental difficulties as well as ambiguities in the interpretation of spectra have inhibited the usefulness of conventional x~ray technique$ for .studying chemical effects. The photoelectron. spectroscopic technique however 1 photo shows much promise in this area. For example; appli?ation ofAelectron spec.troscopy to sodiurn .thiosulfate very directly indicateE\ that there are two dis:tinct . 3 types of.sulfur. atoms present. That is,·the photoelectron spectrum due to the ·sulfur ls 1 ; 2 shell is split into two well-resolved peaks approximately 6 eV -apgrt,the two peaks be...

Modeling the chemical shift of lanthanide4felectron binding energies

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Reactivity of Ozone with Solid Potassium Iodide Investigated by Atomic Force Microscopy

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Multiplet Splitting of Metal-Atom Electron Binding Energies

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