Orbitals and Energies #
Note – these are listed in BINDING ENERGY
Ir 4f ≈ 60 eV
Ir 4s ≈ 690 eV
Ir 4p ≈ 495 eV
Ir 4d ≈ 295 eV
Ir 5s ≈ 95 eV
Ir 5p ≈ 52 eV
Ir 5d ≈ 4 eV
Common Overlaps for Ir 4f #
Pt 4f – Ni 3p – Ra 5d – Cd 4p – V 3s – Xe 4d – Dy 5s – Mo 4s – Co 3p – Th 6s – Na 2s
Theory and Background #
Line Shape Asymmetry #
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Metallic Ir has Doniach–Šunjić (DS) asymmetric tails like Pt and Os due to conduction electron screening.
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Stronger asymmetry in Ir metal compared to Ir oxides → essential to fit with different line shapes, though oxides ARE asymmetric (since they are conductive).
Satellites & Shake-up Features #
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Ir(IV) (IrO₂): Shows distinct satellite peaks about +1.5–2 eV above the main 4f lines.
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These arise from final-state effects (poor screening of the core hole in d⁵ system).
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The intensity of satellites varies with stoichiometry and sample preparation.
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Shake-up / multiplet features: Ir⁴⁺ and Ir³⁺ compounds can show weak shoulders, not easily modeled by simple symmetric functions.
Screening & Final-State Effects #
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Metallic Ir: strong conduction-electron screening → sharp, asymmetric 4f peaks.
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Oxides: reduced screening → broader, more symmetric peaks + satellites.
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Distinguishing factor: metal vs oxide is not just BE shift, but also line-shape and presence/absence of satellites.
Experimental Advice #
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Air stability: Metallic Ir and common oxides (IrO₂) are relatively stable in air. Expect some adventitious C/O contamination.
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Sputtering: Low-energy Ar⁺ sputtering may reduce Ir(IV) → Ir(0). Use carefully, and document effects.
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Heating: In situ heating is usually safe; IrO₂ is thermally robust compared to Os oxides.
Data Analysis Guidance #
HarwellXPS technical director Dr. David Morgan has produced a full work of the analysis of Ir compounds – which can be found at Surface and Interface Analysis, here:
The X-ray photoelectron spectra of Ir, IrO2 and IrCl3 revisited #
The fitting details are as follows:
Iridium Metal
| Peak | B.E. / eV | Area (%) | Doublet Sep. / eV | FWHM / eV | CasaXPS Lineshape |
| 4f7/2 | 60.8 | 57.2 | 3 | 0.84 | LF(0.6, 1, 150, 300) |
| 4f5/2 | 63.8 | 42.8 | 0.86 | LF(0.6, 1, 150, 300) |
IrO2 (anhydrous)
| Peak | B.E. / eV | Area (%) | Doublet Sep. / eV | FWHM / eV | CasaXPS Lineshape |
| 4f7/2 | 61.9 | 49.5 | 3 | 0.7 | LF(0.3, 1, 65, 100) |
| 4f5/2 | 64.9 | 37.1 | 0.75 | LF(0.3, 1, 65, 100) | |
| 4f7/2 (sat) | 63.2 | 7.7 | 3.64 | GL(90) | |
| 4f5/2 (sat) | 66.2 | 5.8 | 3.64 | GL(90) |
IrO2 (hydrated)
| Peak | B.E. / eV | Area (%) | Doublet Sep. / eV | FWHM / eV | CasaXPS Lineshape |
| 4f7/2 | 62.5 | 57.2 | 3 | 1.6 | LF(0.3, 1.5, 25, 150) |
| 4f5/2 | 65.5 | 42.8 | 1.65 | LF(0.3, 1.5, 25, 150) |
IrCl3 (hydrated)
| Peak | B.E. / eV | Area (%) | Doublet Sep. / eV | FWHM / eV | CasaXPS Lineshape |
| 4f7/2 | 62.6 | 60.1 | 3 | 0.94 | LF(1, 1, 55, 200 |
| 4f5/2 | 65.6 | 42 | 1.05 | LF(1, 1, 55, 200 | |
| 4f7/2 (sat) | 71.6 | 1.1 | 1.24 | GL(30) | |
| 4f5/2 (sat) | 74.6 | 0.8 | 1.24 | GL(30) |
References #
- Freakley, Simon J., Jonathan Ruiz‐Esquius, and David John Morgan. “The X‐ray photoelectron spectra of Ir, IrO2 and IrCl3 revisited.” Surface and Interface Analysis 49.8 (2017): 794-799.
