Mossbauer effect quadrupole splitting correlation

Figure 6.6 depicts a comprehensive compilation of isomer shifts for Fe compounds. From this we see a broad correlation between isomer shift and oxidation state, but values also depend on the spin state. Note that high-spin Fe(II) is the only commonly occurring form of iron that can be unequivocally identified by Mossbauer spectroscopy, as all low-spin iron compounds effectively cover the same range of isomer shifts. However, in such cases other Mossbauer hyperfine interactions, such as quadrupole splitting (Section 6.4.2), can help to identify the nature of the iron atom in such compounds. 

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