X‐ray Absorption Spectroscopy


An absorption ‘edge’ is the abrupt increase in absorbance that occurs when the energy of the incident light (typically light in the X‐ray region of the electromagnetic spectrum) exceeds the binding energy of a core electron. X‐ray absorption spectroscopy uses the structured absorption on the high‐energy side of an absorption edge to determine the local structure of the X‐ray‐absorbing atom.

Keywords: EXAFS; XANES; core‐level spectroscopy; electronic‐structure; oxidation state

Figure 1.

Illustration of an XAS spectrum, showing the XANES and EXAFS regions. Inset shows expansion of the XANES region. Data are for a protein containing a [2Fe‐2S] cluster.

Figure 2.

Analysis of EXAFS data. Main figure shows the Fourier transform of data from ; inset shows the isolated EXAFS spectrum. The ‘beat’ (decrease in amplitude) at k = 8 Å−1 is due to the presence of two or more shells of scatterers, as also shown by the presence of two peaks in the Fourier transform.



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Riggs‐Gelasco PJ, Mei R, Yocum CF and Penner‐Hahn JE (1996) Reduced derivatives of the Mn cluster in the oxygen‐evolving complex of photosystem II: an EXAFS study. Journal of the American Chemical Society 118(10): 2387–2399.

Roe AL, Schneider DJ and Mayer RJ et al. (1984) X‐ray absorption spectroscopy of iron‐tyrosinate proteins. Journal of the American Chemical Society 106: 1676.

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Further Reading

Bart JCJ (1986) Near‐edge X‐ray absorption spectroscopy in catalysis. Advances in Catalysis 34: 203–296.

Koningsberger DC and Prins R (1988) X‐ray Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS, and XANES. New York: Wiley.

Penner‐Hahn JE (1988) X‐ray absorption spectroscopy for characterizing metal clusters in proteins: possibilities and limitations. In: Que L Jr (ed.) ACS Symposium Series, pp. 28–48. Washington, DC: American Chemical Society.

Penner‐Hahn JE, Wang S and Waldo GS (1991) Polarized X‐ray absorption spectroscopy of biological molecules. In: Hasnain SS (ed.) X‐ray Absorption Fine Structure, pp. 146–151. New York: Ellis Horwood.

Riggs‐Gelasco PJ, Stemmler TL and Penner‐Hahn JE (1995) XAFS of dinuclear metal sites in proteins and model compounds. Coordination Chemistry Reviews 144: 245–286.

Scott RA (1985) Measurement of metal–ligand distances by EXAFS. Methods in Enzymology 117: 414–459.

Teo BK (1986) EXAFS: Basic Principles and Data Analysis. New York: Springer‐Verlag.

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Penner‐Hahn, James E(May 2005) X‐ray Absorption Spectroscopy. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0002984]