Uranium

Doublet Separations

U 4d: 42.3 eV
U 4f: 10.9 eV
U 5d: 8.2 eV
U 5p: 63.6 eV
U 6p: 10 eV

Available Photoemissions and Energies

The Energies Listed are Binding Energies!

U 4s: 1043 eV
U 4d: 739 eV
U 4f: 380 eV
U 5d: 96 eV
U 6p: 19 eV

Common Element Overlaps

The Energies Listed are Binding Energies!

U is primarily analyzed via the 4f orbital

K 2s (377 eV)
Nb 3p (379 eV)
Hg 4d (379 eV)
Hf 4f (380 eV)
Tl 4d (386 eV)
Tm 4p (386 eV)
Mo 3p (393 eV)
Y 3s (395 eV)
Yb 4p (396 eV)
Tb 4s (398 eV)
N 1s (399 eV)

Augers and Energies

Energies listed are Kinetic Energies!

U OPP: ~ 70 eV

Common Species Binding Energies

The Energies Listed are Binding Energies!

Species	Binding energy / eV	Charge Ref	Ref
U(0)	376.9	Au 4f (83.98 eV)	1
UO₂	380	C 1s (285 eV)	2
UF₃	379.9	Au 4f (83.8 eV)	3
UCl₃	378.1	Au 4f (83.8 eV)	3
UBr₃	378.2	Au 4f (83.8 eV)	3
UF₄	380.0	Au 4f (83.8 eV)	3
UCl₄	380.0	Au 4f (83.8 eV)	3
UBr₄	379.7	Au 4f (83.8 eV)	3
UF₅	382.4	Au 4f (83.8 eV)	3
UCl₅	381.7	Au 4f (83.8 eV)	3
UBr₅	379.5	Au 4f (83.8 eV)	3
UF₆	384.6	Au 4f (83.8 eV)	3
UO₃ ()	382.1	C 1s (285 eV)	4
UO₃ ()	382.0	C 1s (285 eV)	4

Common Uranium Binding Energies

Theoretical calculations predict that U(III), U(IV), and U(V) should exhibit multiplet splitting in their U 4f core-level peaks due to the presence of unpaired 5f electrons.(5,6) This splitting arises from the coupling and recoupling of angular momentum in the ionized core-shell and unpaired valence electrons, leading to multiple final states or peaks in the XPS spectrum.(6)

However, in practice, many XPS studies of monovalent U(V) and U(IV) compounds have failed to reveal significant multiplet structure in the U 4f7/2 line, despite having good energy resolution. Instead, a slight asymmetry on the high binding energy (BE) side is sometimes observed.(6)

The U 4f lines are observed to have relatively narrow primary peaks, the spin-orbit split 4f7/2 and 4f5/2, that do not significantly change shape as a function of oxidation state.

The multiplet splitting is diminished by ligand field effects, and is further reduced by interactions such as covalent mixing and ligand splitting of the 5f, and losses to many-body shake-up satellites.(7) In a solid-state environment, the multiplet splitting of isolated open-shell U cations collapses to below the resolution of conventional high-resolution XPS.(5)

The satellite structures of the U 4f peaks are more useful for determining oxidation states than the primary peaks.

Experimental Advice

XPS Analysis

There may be advantages to analysing the U 5p region, compared to the more commonly measured U 4f orbitals.

Multiplet Splitting Sensitivity: The U 5p lines are theorized to manifest strong multiplet splitting that is sensitive to the oxidation state of uranium. The intensity of the lowest energy multiplet in the 5p core lines increases with decreasing oxidation state, which could provide a clear indication of the uranium’s valence. In contrast, the U 4f lines do not significantly change shape as a function of oxidation state.(5)

Multiplet Structure: The 5d and 5p lines show a low energy multiplet for open shell U(V) and U(IV) spectra, which decreases in intensity from U(IV) to U(V) and is not present for U(VI). This is an important feature for differentiating the oxidation states, whereas the 4f lines do not show such clear distinctions.

Deeper Information Depth: The 5p and 5d lines record signals from slightly deeper within the material than the 4f line because the inelastic mean free path is longer for the higher kinetic energy electrons from the less strongly bound 5p and 5d levels. This could be useful when the surface might not be representative of the bulk material.

Ion Beam Irradiation

If performing depth profiling, or etching studies – take caution as U is known to change state readily when exposed to ion beam irradiation.(8)

Ion beam irradiation can significantly impact uranium-containing materials by changing the oxidation state of uranium, causing structural damage, altering surface composition and modifying the XPS spectra. The magnitude of these effects depends on the ion type, energy, and fluence and the specific material. These effects are relevant in understanding the behaviour of uranium in nuclear fuel and under various environmental conditions.

Fitting Advice

Peak Shape:

The primary U 4f7/2 and U 4f5/2 peaks are relatively narrow.

The shape of the primary U 4f lines does not significantly change with oxidation state and does not carry significant information on the oxidation states, though they may have a slight asymmetry on the high BE side.

For high resolution spectra, the low BE tail of the U 4f7/2 peak may have a more Lorentzian shape for UO2.

In contrast, the 5p and 5d lines do show significant changes in peak shape as a function of the oxidation state due to multiplet splitting.(6)

Satellite Structures:

The use of satellites can better distinguish U oxidation states than BEs alone.

Uranium oxides exhibit shake-up satellites.(2,8) These satellites appear at higher BE than the main peaks.

The energy separation (ΔEs-p) between the primary peaks and their associated satellites is a key parameter for determining oxidation states because it is relatively insensitive to composition/structure.(6,7)

U(IV) satellites appear around 7 eV from the main peak, U(V) satellites appear around 8 eV from the main peak, and U(VI) satellites appear at about 4 eV and 10 eV. Note that the U 4f7/2 ~10 eV satellite is not usually reported because it is buried under the primary U 4f5/2 peak.(6,8)

Satellite intensities can also be indicative of the oxidation state. U(IV) satellites typically have about 30% of the total U 4f intensity, U(V) about 20% and U(VI) about 10-15%.(6)

It is important to include satellite peaks, particularly for low energy resolution conditions, as they are likely to be resolved even though the primary peaks are not.(6) In cases where two or more oxidation states have similar U 4f BEs and are strongly overlapped, including the satellite peaks is imperative.(6)

When fitting mixed valence systems it is helpful to fix the ΔEs-p and satellite/primary peak intensity ratios based on reference materials.(6)

XPS Spectra Uranium (U) Compounds, xpsdatabase.com, B Vince Crist, https://xpsdatabase.com/uranium-spectra-u-metal-uranium-metal/, accessed 06/01/2025
Maslakov, Konstantin I., et al. “XPS study of the surface chemistry of UO2 (111) single crystal film.” Applied Surface Science 433 (2018): 582-588. Read it online here.
Thibaut, Elisabeth, et al. “Electronic structure of uranium halides and oxyhalides in the solid state. An x-ray photoelectron spectral study of bonding ionicity.” Journal of the American Chemical Society 104.20 (1982): 5266-5273. Read it online here.
Allen, Geoffrey C., and Nigel R. Holmes. “Surface characterisation of α-, β-, γ-, and δ-UO 3 using X-ray photoelectron spectroscopy.” Journal of the Chemical Society, Dalton Transactions 12 (1987): 3009-3015. Read it online here.
Ilton, Eugene S., et al. “Quantifying small changes in uranium oxidation states using XPS of a shallow core level.” Physical Chemistry Chemical Physics 19.45 (2017): 30473-30480. Read it online here.
Ilton, Eugene S., and Paul S. Bagus. “XPS determination of uranium oxidation states.” Surface and Interface Analysis 43.13 (2011): 1549-1560. Read it online here.
Bagus, Paul S., Connie J. Nelin, and Eugene S. Ilton. “Theoretical modeling of the uranium 4f XPS for U (VI) and U (IV) oxides.” The Journal of Chemical Physics 139.24 (2013). Read it online here.
Teterin, Yury A., et al. “XPS study of ion irradiated and unirradiated UO2 thin films.” Inorganic chemistry 55.16 (2016): 8059-8070. Read it online here.

Initial vs Final State Effects

Multiplet Splitting

Multiplet splitting of s-orbitals in first row transition metals

Peak Asymmetry in Conducting Materials

Photoionisation Cross Sections

Spin-Orbit Splitting

The Auger, or Auger-Meitner, Process and Auger Peaks

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Uranium

XPS Analysis

Ion Beam Irradiation