Binding Energy in Practice An Issue

For the purpose of catalyst analysis, the weaknesses of ESCA turn into strengths as it is the chemical bonding of the outer surface of a solid that is of interest and only to a lesser extent its bulk chemical structure. Most of our theoretical understanding of chemical bonding refers, however, to the bulk state (crystal structures) 

The quantities contributing to the position of a photoelectron (PE) line in solids can be summarized by the following equation  

Detailed treatments of this issue can be found in the Hterature [3, 14, 15]. Here we only briefly review the contributions under prachcal considerations and without discussing the deep quantum chemical implications involved. 

The excitation energy (Ehv) should be as monochromatic as possible to maximize the resolution of the experiment. The kinetic energy Efj is the direct experimental result of the PE experiment. It is used as energy scale in Auger spectroscopy but today no longer in PE spectra. Note that this is not the case in older literature where often the kinetic energy was plotted. 

The term Ed, stands for charging contributions. This term is absent in spectra of samples exhibiting a finite density of states at the Eermi level. For all practical purposes this is correct for aU true metals and for many semiconductors with intrinsic states near zero binding energy. Many systems relevant in catalysis do, however, not fulfill this condition (all non-black samples, glasses, porous materials, supports) or even worse, are composites of metallic and non-metaUic systems, giving rise to mixed metalhc-insulating behavior of their surface under PES. Such 

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