I read somewhere that EXAFS (Extended X-ray absorption fine structure) gives us the distances between central atom and its neighboring atoms. Is that true? Why can't we get the distance between two atoms, which none of them are central? How is EXAFS method distinguishing between central atom and other ones? So for example for CF4, I think we get one EXAFS peak for C...F distance and not F...F distance, why?


(Copied and edited from comments)

The central atom here refers to the center of attention (i.e. where the given peak assigned), the center of scattering which is often a center of an active site/coordination complex. I.e anything can be a central atom, if you tune your X-ray frequency to their peaks - you choose the central atom. In the given example theoretically you can choose to study C or F, and their closes neighbors. Theoretically you can see their neighbors; C-F distance is much shorter than F..F distance, though.

You should understand the use/limitations of the method: if you have chemically nonequivalent atoms of the same type in your sample, you will have their EXAFS peaks overlap. Both will give you a signal at the same place, which are hard to separate. In practice it means that you can use this analysis for e.g. central metal atom of complexes, but not for carbon atoms of a ligand as you generally have a lot of different carbon atoms in the sample.

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