Binding energy of core electrons

In X-ray photoelectron spectroscopy (XPS or X-PES), the irradiation (usually a Mg K a (1253.6 eV) or A1K a (1486.6 eV) source) causes a core electron to be ejected. This is a more useful technique than UPS for surface studies, since the binding energies of core electrons are characteristic of the elements in question and surface elements can thus be identified by the traditional spectroscopic fingerprinting procedure. In this respect, XPS is sometimes referred to by its alternative name, electron spectroscopy for chemical analysis (ESCA). In order to emphasis the contribution from surface atoms, the X-ray beam is usually set at a grazing angle to the surface. Most of the signal originates from within a nanometre of the surface. 

The application of ESCA to the investigation of aromaticity is based on the known sensitivity of the binding energies of core electrons to... 

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