Adsorption site identification in surface extended x-ray absorption fine structure

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Abstract
Adsorption sites and adsorbate–substrate bondlengths are usually deduced from surface extended x-ray absorption fine structure (EXAFS) by a Fourier filtering approach. We discuss here the merits and problems of an alternative method involving simulations of the EXAFS which include the role of several scattering shells. With the aid of specific examples we show that even in simple cases this approach can add to or reinforce the normal structural conclusions but in the case of overlapping contributions from two or more bondlengths the simulation approach is the only one which is truly satisfactory. Molecular adsorbates, such as formate (HCOO), will invariably suffer from this difficulty due to the mismatch of intramolecular and intrasubstrate bondlengths, forcing individual atoms in the molecule to adopt low-symmetry adsorption sites.

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