XANES
Also known as: XANES spectroscopy, near-edge X-ray absorption
X-ray Absorption Near Edge Structure (XANES) is a synchrotron X-ray spectroscopy technique that measures the electronic and geometric structure around a specific atom by analyzing the X-ray absorption spectrum within about 50 eV of an absorption edge. Developed by Lee and Pendry in 1975, XANES is complementary to EXAFS and reveals valence state, local symmetry, and unoccupied orbital structure through near-threshold features and resonances.
Key highlights
- Rapid acquisition: XANES scans complete in minutes, ideal for time-resolved in situ studies
- Valence state sensitivity: edge position and white line intensity directly report oxidation state
- Local symmetry information: crystal field effects and coordination geometry encoded in XANES features
- Quantitative: XANES can be used for fingerprinting and rapid phase identification
Intuition
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How it works
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When to use it
Apply XANES to determine valence state, local symmetry, and electronic structure around a specific atom in any sample: catalysts, minerals, environmental samples, and biological systems. XANES is faster and simpler than EXAFS and requires no extensive data analysis. Requires synchrotron access.
Strengths & limitations
- Rapid acquisition: XANES scans complete in minutes, ideal for time-resolved in situ studies
- Valence state sensitivity: edge position and white line intensity directly report oxidation state
- Local symmetry information: crystal field effects and coordination geometry encoded in XANES features
- Quantitative: XANES can be used for fingerprinting and rapid phase identification
- Low spatial resolution compared to EXAFS; typically probes 3-5 Ångströms
- Interpretation requires comparison to standards or calculations; absolute structure determination not possible
- Overlapping absorption edges from different elements can confound interpretation
- Synchrotron access required; technique not accessible at laboratory X-ray sources
Common pitfalls
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Applications
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Frequently asked
How does XANES reveal oxidation state?
X-ray absorption edge position shifts to higher energy as oxidation state increases (electrons are more tightly bound). Additionally, the intensity of the white line (resonance just above the edge) is proportional to the number of unoccupied d-orbitals, which decreases with increasing oxidation state. These features together provide strong oxidation state sensitivity.
What is the white line in XANES?
The white line is an intense resonance just above the X-ray absorption edge, arising from transitions to unoccupied orbitals (e.g., d-orbitals). Its intensity correlates with the number of d-holes (unfilled d-orbital vacancies). For transition metals, the white line intensity tracks oxidation state.
Can XANES distinguish between different crystal structures?
Partially, yes. Different crystal structures with the same atom have different local symmetries, which affects XANES features. However, EXAFS is more powerful for structure determination; XANES is better for oxidation state and symmetry.
Sources
- 1.Lee, P. A., & Pendry, J. B. (1975). Theory of extended x-ray absorption fine structure. Physical Review B, 11(8), 2795-2811.
- 2.Koningsberger, D. C., & Prins, R. (Eds.). (1988). X-ray Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS, and XANES. John Wiley & Sons.
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Cite this page
ScholarGate. (2026, June 3). XANES. ScholarGate. https://scholargate.app/spectroscopy/xanes