• One obvious way in which an atom may change is by changing oxidation state
• If a metal centre transitions from it’s zero-valent form to it’s ionized form upon complexation with an anion/ligand it will obtain an overall positive charge
• Since electron density has been removed, the nucleus will now exert a greater pull upon the remaining electrons – effectively increasing the binding energy
• As well as oxidation state, the neighbouring atoms play a role in determining the binding energy of a core orbital
• Tungsten atoms with the same oxidation state may show differing binding energies
• Electronegative ions withdraw electron density from the target atom – producing a positive dipole and increasing the binding energy of the core orbital

• Auger peaks are secondary electron emissions
• Following a photoemission, electrons in higher energy orbitals may relax to fill the newly created core-hole
• This relaxation releases energy in the form of X-rays
• These X-rays may then excite another electron to the point of photoemission

• Due to the nature of Auger electrons, they tend to be more affected by changes to the valence structure (i.e. bonding) than core orbitals
• One way this can be of use is the Auger parameter
• This involves subtracting the kinetic energy of the related core orbital from that of the auger emission

α = EK(Auger) – EK(Core)

• This was later developed into the modified Auger parameter in order to be independent of excitation energy
• The parameter may be used to probe oxidation states where core level spectroscopy cannot

α’ = EK(Auger) + EB(Core)