Revisiting the electron affinity of selenium

Chuangang Ning; Jiayi Chen; Qihan Liu; Rui Zhang; Wenru Jie

REVIEW 4 major objections 3 minor 4 references

Revisiting the electron affinity of selenium

T0 review · 4 major / 3 minor · reviewed 2026-08-07 · deepseek-v4-flash

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Pith's one-line read The paper re-measures the electron affinity of selenium with slow-electron velocity-map imaging and concludes that the 2012 laser microscopy value is 0.50 cm−1 too low, recommending a revised EA of 16,297.78(4) cm−1.

desk verdict New SEVI measurement of EA(Se) is plausible and internally consistent, but the absolute calibration is too thinly documented to overturn the LPM benchmark yet. read the letter →

arxiv 2506.10300 v1 pith:VHXD3DDP submitted 2025-06-12 physics.atom-ph

Rui Zhang , Wenru Jie , Jiayi Chen , Qihan Liu , Chuangang Ning This is my paper · ORCID

classification physics.atom-ph

keywords electronaffinityseleniumslow-electronvelocity-mapimaginglaserphotodetachmentmicroscopythresholdisotopeshiftnegativeionfinestructure

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper re-measures the electron affinity of atomic selenium with slow-electron velocity-map imaging (SEVI) and argues that the value accepted for more than a decade, 16,297.276(9) cm−1 from laser photodetachment microscopy (LPM), is about 0.5 cm−1 too low. The authors report a revised value of 16,297.78(4) cm−1, matching older laser photodetachment threshold (LPT) measurements with ten times better precision. Isotope-resolved measurements and an independent transition that reproduces the known 3P2–3P1 splitting of neutral selenium are used to support the new value. If correct, this settles a long-standing discrepancy and shifts a reference constant used in atomic and molecular physics.

What carries the argument

The central object is the slow-electron velocity-map imaging (SEVI) measurement, in which the kinetic energy of threshold photoelectrons is obtained from the radius of the reconstructed spherical image. The argument is carried by a linear regression of photon energy hν against squared radius r2; the vertical intercept is the binding energy, so the electron affinity comes from the threshold extrapolation rather than from a single spectrum. Cross-checks include measuring five selenium isotopes at two imaging voltages and measuring a second photodetachment transition whose energy difference with the first reproduces the known neutral 3P2–3P1 interval.

What would settle it

Re-measuring the electron affinity of selenium with an independent method, such as photodetachment microscopy with a calibrated electric field, and obtaining 16,297.276(9) cm−1 within its claimed uncertainty would contradict the revised value. More directly, running the same SEVI measurement at several imaging voltages, including −50 V and −200 V, and finding that the fitted intercept shifts by about 0.2 cm−1 would show that the two-voltage test missed a field-dependent systematic.

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Extended reading notes

Core claim

Using a cryogenic SEVI apparatus, the authors photodetach mass-selected Se− ions and image slow electrons. A linear fit of photon energy against the squared image radius gives the binding energy of the ground-to-ground transition Se(3P2) ← Se−(2P3/2) as 16,297.78(4) cm−1, which is the electron affinity. They reproduce this value from a second transition that, combined with the NIST 3P2–3P1 splitting, yields 16,297.78(5) cm−1, and they find no isotope shift larger than 0.03 cm−1. They conclude that the 2012 LPM result deviates by 0.50 cm−1, fifty times its claimed uncertainty, and recommend the SEVI/LPT-consistent value.

Load-bearing premise

The conclusion that the previous laser microscopy value is wrong rests on the assumption that testing only two imaging voltages, −75 V and −150 V, is enough to rule out a field-dependent energy shift in the SEVI measurement; if the shift varies nonlinearly or appears at other field settings, the electron affinity could move by up to about 0.2 cm−1.

Editorial extensions

If this is right

The recommended electron affinity of selenium becomes 16,297.78(4) cm−1 (2.020667(5) eV), replacing the 2012 value as the reference.
The long-standing disagreement between LPM and LPT results for selenium is resolved in favor of the older LPT measurements.
The 3P2–3P1 splitting derived from the two transitions, 1989.50(7) cm−1, agrees with the spectroscopic reference 1989.497 cm−1, independently validating the energy scale.
Selenium isotope shifts in electron affinity are below 0.03 cm−1, consistent with the new value being isotope-independent within uncertainty.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The paper's two-voltage check is a reasonable but limited test; a full field-dependence scan would make the exclusion of the alleged 'quantum offset' more conclusive, since a nonlinear voltage dependence could survive the two-point check.
If the LPM systematic error in selenium is real, other LPM electron affinities measured under similar field conditions may carry undetected shifts of comparable size and could be worth rechecking.
A high-level relativistic quantum calculation of EA(Se) near 16,297.8 cm−1 would provide a theory-side check that is independent of both imaging and threshold methods.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Bottom line: this is a credible remeasurement that could well be right, but the absolute energy scale is not established tightly enough to sustain the 0.04 cm-1 claim against the LPM benchmark.

What's genuinely new: a direct SEVI measurement of EA(Se) with 0.04 cm-1 stated uncertainty, plus isotope-resolved measurements and a cross-check through the neutral 3P2-3P1 splitting. The internal consistency is good; the isotope values cluster within ~0.03 cm-1, and the splitting from transitions A and B reproduces the NIST value to within 0.007 cm-1. The final value agrees with the older LPT measurements and sits 0.50 cm-1 above the 2012 LPM result—fifty times the claimed uncertainty of the latter. That alone makes the paper worth taking seriously.

The soft spot is the absolute calibration. The EA is the intercept of hν versus αr2. Any constant offset in the kinetic-energy scale—whether from a 'quantum offset' or just an imperfect radius-to-energy calibration—moves the intercept by that same amount. The paper's test is to compare imaging voltages of -75 V and -150 V and see no change. That excludes a large field-dependent offset, but not an offset that saturates, is voltage-independent, or depends on the ion cloud or laser alignment. The alternative-channel check using transition B and the NIST splitting only validates relative energies: a common-mode shift cancels. So the 0.2 cm-1 quantum offset discussed in Ref. [32] is not actually ruled out by the data presented, and if it were present it would shift the recommended value by five times the stated error.

The paper also gives no raw data and does not describe how α was calibrated for each voltage setting. That is a fixable omission, but it is central to the claim.

Who this is for: atomic physics and anyone using EA benchmarks in thermochemical or spectroscopic databases. The paper deserves a serious referee. I would ask for the calibration procedure, the raw spectra, and a more systematic voltage-dependence study—ideally testing three or four voltages and validating the energy scale on a reference transition with a known electron affinity. If the absolute scale holds up, the correction to the LPM value is real. As it stands, the evidence is suggestive, not conclusive.

Referee Report

4 major / 3 minor

Summary. The paper reports a new measurement of the electron affinity (EA) of atomic selenium using slow-electron velocity-map imaging (SEVI). By tuning the detachment laser slightly above the threshold for Se(3P2) ← Se−(2P3/2) and fitting the photon energy versus the squared photoelectron radius, the authors extract the binding energy as the intercept and obtain EA(Se) = 16,297.78(4) cm⁻¹. This value is consistent with earlier LPT measurements but is 0.50 cm⁻¹ higher than the 2012 LPM value of 16,297.276(9) cm⁻¹. Cross-checks include measurements on five selenium isotopes, a comparison at two imaging voltages, and an alternative transition B whose difference from transition A yields the known 3P2–3P1 splitting of neutral Se. The paper recommends a revised reference value of 16,297.78(4) cm⁻¹ for EA(Se).

Significance. If the absolute calibration issue is resolved, this is an important metrology result: it directly challenges a decade-long reference standard, is consistent with older LPT values, and improves precision by an order of magnitude over those LPT measurements. The isotope consistency and the independent verification of the 1989.497 cm⁻¹ fine-structure splitting are genuine strengths that support the internal consistency of the measurements. However, the central claim hinges on the absolute accuracy of the SEVI kinetic-energy scale near threshold, and the evidence presented for that absolute accuracy is thin, as detailed in the major comments.

major comments (4)

[Precise measurement of the electron affinity of Se (Fig. 2, Eq. hν = BE + αr²)] The calibration coefficient α and its determination are not described. The EA is the intercept of the linear fit hν = BE + αr², so any constant offset in the kinetic-energy scale (e.g., r² → r² + r0² or Ek → Ek + E0) is absorbed into the intercept and shifts the EA by αr0² or E0. To substantiate the claimed 0.04 cm⁻¹ accuracy, the authors must specify how α was calibrated (e.g., using known photodetachment lines, electrostatic simulations, or a separate measurement) and include its uncertainty in the final error budget.
[Table I and the two-voltage test (-75 V vs -150 V)] The exclusion of the 'quantum offset' of Ref. [32] rests on comparing only two imaging voltages. This test can detect an offset that scales strongly with voltage, but it cannot exclude a voltage-independent common-mode offset, a nonlinear or saturating offset, or a species-specific component. The authors should either provide a quantitative bound on any residual offset from measurements at several voltages or against a reference transition with a known absolute energy, or explicitly weaken the claim that the 'quantum offset' is excluded.
[Verification via an alternative transition (Fig. 3)] The alternative-transition verification validates only the relative energy difference between transitions A and B. Any common-mode shift of all measured binding energies cancels in the subtraction, so the agreement with the NIST 3P2–3P1 splitting of 1989.497 cm⁻¹ does not by itself validate the absolute EA value. The paper should clarify that this check is a consistency test of relative energies, not an absolute calibration.
[Uncertainty budget (stated ±0.04 cm⁻¹)] The paper states that the total uncertainty of 0.04 cm⁻¹ includes a 0.02 cm⁻¹ contribution from the wavelength meter, but it does not provide a complete uncertainty budget. Missing terms include the statistical uncertainty of the linear-fit intercept, the uncertainty in α, possible residual field offsets, the extrapolation to r² = 0, and any contribution from the two-voltage test. A full propagation of uncertainties is necessary to support the quoted 0.04 cm⁻¹ error bar.

minor comments (3)

[Throughout] There are typographical inconsistencies, including 'serval natural isotopes' instead of 'several natural isotopes', and the spelling 'Vandevrage' appears in the text while the reference list uses 'Vandevraye'.
[Fig. 4 caption] The black dashed line representing the recommended weighted value is not defined in the caption, and the weighting procedure for combining SEVI and LPT measurements is not described in the main text.
[Raw data] The raw data for the linear fits (photon energies and corresponding r² values) are not provided, which limits reproducibility; a table of fit points or a supplementary data file would be helpful.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the EA(Se) value is obtained as an intercept on an externally calibrated photon-energy scale, with independent cross-checks against NIST fine-structure data and isotope measurements.

full rationale

The derivation chain is self-contained with respect to circularity. The central value EA(Se) = 16,297.78(4) cm−1 is extracted from the linear regression hν = BE + αr², where hν comes from an external wavelength meter calibrated at 0.02 cm−1 accuracy and r² is the measured electron-sphere radius; the intercept is not constrained by any prior EA(Se) value. The paper does not fit a parameter to a subset of Se EA data and then predict a closely related quantity; rather, it measures transitions A, B, and C independently. The alternative-transition check uses the NIST 3P2–3P1 splitting, an external benchmark, to validate the relative energy scale, while the isotope measurements test internal consistency. The discussion of the 'quantum offset' and the two-voltage comparison concerns systematic uncertainty in the absolute calibration, not a definitional equivalence; even if the two-voltage test is insufficient to exclude a field-dependent offset, that is a correctness or rigor concern, not circularity. Self-citations to the group's previous SEVI apparatus papers are methodological references, not load-bearing arguments that define the target value in terms of itself. No step in the paper reduces by construction to its own inputs, so the circularity score is 0.

Assumptions & free parameters 1 free parameters · 4 assumptions · 0 invented entities

The central measurement rests on the assumed linear energy-radius relation for the velocity-map imager, the accuracy of the NIST fine-structure splitting used for cross-checks, the purity of the assigned transitions, and the adequacy of a two-voltage test to exclude a field-dependent systematic. These are stated or implied in the Experimental Methods and verification sections.

free parameters (1)

Calibration coefficient alpha = not reported in the letter
Converts measured squared image radius to electron kinetic energy in the relation hν = BE + αr^2; the paper does not state whether it is calibrated externally or fitted simultaneously with the intercept.

assumptions (4)

domain assumption The kinetic energy of detached electrons is exactly proportional to the squared image radius, E_k = αr^2, over the relevant energy range.
Used to convert measured radii to binding energies in Figure 2 and Figure 3 fits.
domain assumption The neutral Se 3P2-3P1 splitting is 1989.497 cm-1 as given by NIST/Eriksson.
Used to verify EA(Se) from transition B.
domain assumption Changing the imaging voltage from -75 V to -150 V is a sufficient test for the field-dependent quantum offset claimed by Blondel and Drag.
The paper uses the null result of this two-point test to dismiss the quantum-offset criticism.
domain assumption The observed photoelectron peaks correspond to the assigned transitions with no significant contamination from SeH- or other species.
Assignment of peaks A-C in Figure 1 and interpretation of isotope data rely on spectral purity.

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Cite this review

Pith. "Pith review of Revisiting the electron affinity of selenium." pith.science (2026). https://pith.science/paper/VHXD3DDP

@misc{pith2026250610300,
  author       = {Pith},
  title        = {Pith review of: Revisiting the electron affinity of selenium},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/VHXD3DDP}},
  note         = {Machine review of arXiv:2506.10300}
}

read the original abstract

The electron affinity (EA) of atomic selenium, previously established as 16,297.276(9) cm-1 based on the laser photodetachment microscopy (LPM) measurements in 2012, exhibited a significant deviation from other earlier experimental values, yet it remained the accepted reference standard for over a decade. In this letter, we re-examined the EA of Se using the slow-electron velocity-map imaging method and revealed a substantial deviation in the LPM result. Measurements for the different isotopes of Se and the energy-level splitting of the neutral Se atom's 3P2 - 3P1 further verified the accuracy and robustness of our SEVI method. Based on these experimental evidences, we recommended a revised EA(Se) value of 16,297.78(4) cm-1, which is in excellent agreement with the previous laser photodetachment threshold (LPT) experimental results.

Figures

Figures reproduced from arXiv: 2506.10300 by the authors.

**Figure 2.** FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗

**Figure 4.** FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗

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Reference graph

Works this paper leans on

4 extracted references · 4 canonical work pages

[1]

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H. Hotop, T. A. Patterson, and W. C. Lineberger, High-Resolution Photodetachment Study of Se− Ions, Phys. Rev. A 8, 762 (1973). [11] N. B. Mansour, C. J. Edge, and D. J. Larson, Laser photodetachment spectroscopy of Se− and S−, Nucl. Instrum. Methods Phys. Res., Sect. B 31, 313 (1988). [12] J. Thøgersen, L. D. Steele, M. Scheer, H. K. Haugen, P. Kristense...

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Pith tools

Reviewed August 7, 2026 · model on record in the stance chip above.

[1] [1]

Andersen, Atomic negative ions: structure, dynamics and collisions, Phys

T. Andersen, Atomic negative ions: structure, dynamics and collisions, Phys. Rep. 394, 157 (2004). [2] W. C. Lineberger, Once upon Anion: A Tale of Photodetachment, Annu. Rev. Phys. Chem. 64, 21 (2013). [3] J. C. Rienstra-Kiracofe, G. S. Tschumper, H. F. Schaefer, S. Nandi, and G. B. Ellison, Atomic and Molecular Electron Affinities: Photoelectron Experim...

work page 2004

[2] [5]

Hotop and W

H. Hotop and W. C. Lineberger, Binding Energies in Atomic Negative Ions: II, J. Phys. Chem. Ref. Data 14, 731 (1985). [6] T. Andersen, H. K. Haugen, and H. Hotop, Binding Energies in Atomic Negative Ions: III, J. Phys. Chem. Ref. Data 28, 1511 (1999). [7] C. Ning and Y. Lu, Electron Affinities of Atoms and Structures of Atomic Negative Ions, J. Phys. Chem...

work page 1985

[3] [10]

Hotop, T

H. Hotop, T. A. Patterson, and W. C. Lineberger, High-Resolution Photodetachment Study of Se− Ions, Phys. Rev. A 8, 762 (1973). [11] N. B. Mansour, C. J. Edge, and D. J. Larson, Laser photodetachment spectroscopy of Se− and S−, Nucl. Instrum. Methods Phys. Res., Sect. B 31, 313 (1988). [12] J. Thøgersen, L. D. Steele, M. Scheer, H. K. Haugen, P. Kristense...

work page 1973

[4] [26]

A. T. J. B. Eppink and D. H. Parker, Velocity map imaging of ions and electrons using electrostatic lenses: application in photoelectron and photofragment ion imaging of molecular oxygen, Rev. Sci. Instrum. 68, 3477 (1997). [27] I. León, Z. Yang, H.-T. Liu, and L.-S. Wang, The design and construction of a high-resolution velocity-map imaging apparatus for...

work page 1997