We will next present two examples, which we will follow for the rest of this chapter.
12.1.1 Example: Which Ligand? Consider an unknown iron compound in a soil sample, for which we have collected EXAFS data at the iron K edge. It is known that there is a fairly high sulfur content in the soil, and there is plenty of oxygen as well. As a researcher, we are interested in discovering whether the iron is bonded primarily to sulfur, to oxygen, or to a mix of the two; that is our primary question. (A mix would not necessarily mean that an individual iron atom had ligands of both types-it might mean that some iron was present in the form of a sulfide and some in the form of an oxide.)
Secondary questions might include a more specific identification of the iron phases that are present (e.g., which of the many possible iron oxides are present?), and an estimate of the fraction of each iron mineral present, if it does turn out there is a mixture.