Pith. sign in

REVIEW 4 major objections 4 minor 39 references

Superoxide anion (O$_{2}\negthinspace^{-}$) collisions with CO$_{2}$ molecules in the energy range 50-950 eV

T0 review · 4 major / 4 minor · reviewed 2026-08-10 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read The paper reports the first absolute total electron detachment cross sections for O2− + CO2 between 50 and 950 eV, and assigns high-mass cations CO3+ and CO4+ to a double-ionization pathway.

desk verdict First absolute TEDCS for O2– + CO2 are worth a serious look, but the relative TICS table has suspicious duplicates and the absolute cross sections depend on an unquantified beam-purity assumption. read the letter →

arxiv 2501.08107 v1 pith:TZ6L55DP submitted 2025-01-14 physics.chem-ph physics.atom-ph

C. Guerra , M. Leiferman , A.I. Lozano , F. Aguilar-Galindo , S. Díaz-Tendero , J. C. Oller , P. Limão-Vieira , G. García This is my paper · ORCID
classification physics.chem-phphysics.atom-ph
keywords absoluteelectrondetachmentcrosssectionsuperoxideanionCO2collisionstotalionizationtime-of-flightmassspectrometryanion-inducedfragmentationCO3+cationCO4+
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 sets out to measure, for the first time, absolute total electron detachment cross sections for superoxide anions (O$_2^-$) colliding with CO$_2$ molecules at impact energies from 50 to 950 eV. It also reports relative total and partial ionization cross sections and identifies new cationic products with masses above the CO$_2$ parent ion appearing above about 500 eV. Because only low-energy reaction studies previously existed for this projectile–target pair, these data fill a long-empty column in anion–CO$_2$ collision physics. The broader interest is that O$_2^-$ is a reactive oxygen species and CO$_2$ appears in atmospheric, plasma, and biological settings, so quantitative cross sections are needed to model how such anions transfer charge and energy.

What carries the argument

The load-bearing experimental machinery is a hollow-cathode anion source feeding a gas cell of known effective length (36 mm) and pressure, where the transmitted O$_2^-$ current obeys the Beer–Lambert law $e^{-P l \sigma_t/(k T)}$; the slope of the semilogarithmic attenuation curve versus CO$_2$ pressure yields the absolute total electron detachment cross section. On the ion-detection side, extractive pulsed plates and a 1.40 m time-of-flight mass spectrometer assign masses to the positive ions, while a retarding-field analyzer checks the primary beam energy. The interpretative machinery is quantum-chemistry exploration of the potential energy surfaces at the MP2 and CCSD(T)/aug-cc-pVTZ levels, which identifies the low-lying structures and enthalpy differences that support the CO$_2^{2+}$ + O$_2^-$ $\to$ [CO$_2\cdot$O$_2$]$^+$ $\to$ CO$_4^+$/CO$_3^+$ mechanism.

What would settle it

Mass-select or isotopically label the primary beam at the gas-cell entrance and repeat the attenuation measurement: if the absolute detachment cross section extracted from the Beer–Lambert relation changes by more than the stated $8\text{–}10\%$ uncertainty, the assumption that the beam is effectively pure O$_2^-$ is wrong. Alternatively, run the collision below the CO$_2$ double-ionization threshold and look for the mass-to-charge features at 60–64 and 74–76; the proposed mechanism predicts they should disappear when CO$_2^{2+}$ cannot be formed.

Watch

Extended reading notes

Core claim

On the authors' account, the central discovery is that O$_2^-$ + CO$_2$ collisions in the 50–950 eV range have a measurable absolute electron-detachment cross section that stays near $2.2\times 10^{-20}$–$2.5\times 10^{-20}\,\mathrm{m}^2$ with a shallow dip near 250 eV and a shoulder near 400 eV, and that above roughly 500 eV the collision produces unexpected high-mass cations assigned to (CO$_2\cdot$O)$^+$ and (CO$_2\cdot$O$_2$)$^+$, i.e. CO$_3^+$ and CO$_4^+$. The proposed formation path is sudden double ionization of CO$_2$ followed by electrostatic attraction of the resulting CO$_2^{2+}$ dication to the incoming O$_2^-$, or evolution of highly excited [CO$_2\cdot$O$_2$]$^+$ states into covalently bound CO$_4^+$ structures. Quantum-chemistry scans of the neutral, anionic, and cationic potential energy surfaces place these high-mass channels about $12\text{–}21$ eV above the entrance channel, consistent with a double-ionization threshold.

Load-bearing premise

The absolute cross sections rest on the beam reaching the gas cell being essentially pure O$_2^-$; any surviving O$^-$ or O$_3^-$ would blend several detachment cross sections into one attenuation curve.

Editorial extensions

If this is right

  • If the measurements are correct, the Table II values provide the first absolute benchmark for O$_2^-$ + CO$_2$ and can be used directly in models of CO$_2$-rich plasmas and atmospheres.
  • The relative total ionization cross section profile, with local maxima near 350 and 700 eV, indicates that ionization channels open in at least two energy windows, with the 700 eV peak carried mainly by CO$_3^+$ and CO$_4^+$ formation.
  • Assigning the mass-to-charge features at 60–64 and 74–76 to projectile–target cations means that a single anion impact above the double-ionization threshold can synthesize stable oxygen-rich CO$_x^+$ species.
  • The comparison showing higher-mass fragmentation for anion impact than for electron impact at the same 600 eV energy implies that the O$_2^-$ projectile accesses reaction pathways that a simple electron-equivalent energy deposit does not.

Reading between the lines

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

  • Beyond the paper, the same double-ionization-then-electrostatic-attraction mechanism should be testable with other anionic projectiles against CO$_2$; observing the high-mass features whenever the collision energy exceeds the target double-ionization threshold would generalize the picture.
  • The near alignment of the 400 eV detachment shoulder with the 350 eV ionization maximum suggests a shared onset; a coincidence measurement of ejected electrons and product cations could test whether the detachment rise comes specifically from double-ionization channels.
  • Isotope-labelled collisions, such as $^{18}$O$_2^-$ with C$^{16}$O$_2$, would reveal whether the extra oxygen atoms in CO$_3^+$/CO$_4^+$ come from projectile or target, distinguishing the electrostatic-capture mechanism from ordinary atom transfer.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 4 minor

Summary. The paper reports a combined experimental and theoretical study of O2− collisions with CO2 in the 50–950 eV impact-energy range. Absolute total electron detachment cross sections (TEDCS) are obtained from gas-cell beam-attenuation measurements via the Beer–Lambert law, and relative total and partial ionization cross sections are derived from time-of-flight mass spectra of the positive fragments. For projectile energies above about 500 eV, cations with m/z above the parent CO2+ ion are observed and tentatively assigned to (CO2·O)+ and (CO2·O2)+, i.e., CO3+ and CO4+. Complementary MP2 and CCSD(T) calculations map the relevant potential-energy surfaces and support a mechanism in which target double ionization is followed by electrostatic attraction between CO2^2+ and O2−, forming the high-mass cationic complexes.

Significance. If the measurements are reliable, this is the first absolute TEDCS data set for O2− + CO2 in the intermediate-energy range, which could be valuable for modeling anion-driven chemistry in plasmas and planetary atmospheres. The paper also presents a plausible and energetically grounded mechanism for the formation of CO3+ and CO4+ collision products, and the quantum-chemistry part uses standard, well-defined methods. The experimental section contains a clear uncertainty budget for the TEDCS and the paper is generally written so that the claims can be checked. However, the absolute TEDCS claim depends on an unverified beam-purity assumption, and the relative TICS table contains duplicate numerical values that strongly suggest a data-handling error. These issues are load-bearing for the paper's central conclusions and currently prevent endorsement of the results as presented.

major comments (4)
  1. [Sec. 2.1, 2.2a; Eq. (1)] The absolute TEDCS claim in Sec. 5 rests on Eq. (1), where the attenuation slope is attributed entirely to O2− + CO2 electron detachment. Section 2.1 states that the projectile beam 'is mainly formed by O2− but also contains certain amounts of O−, and O3−', and the TOF filtering described there is applied to the extractive-pulse system used for the positive-fragment mass analysis, not to the continuous transmitted beam counted by MCP2. If O− or O3− survive in the transmitted beam, the measured exponential slope is a mixture of detachment cross sections for several projectile species. The uncertainty analysis in Sec. 2.2b includes statistical, pressure, and path-length terms but no beam-purity term. Please provide a mass spectrum of the primary beam as detected by MCP2, or otherwise demonstrate that the transmitted beam is effectively pure O2−, or quantify the O− and O3− fractions and their effect on the reported TEDCS values.
  2. [Table III] The relative TICS values contain exact duplicates at widely separated energies with different associated uncertainties: 230 and 850 eV both give 1.22; 250 and 900 eV both give 6.93; 570 and 730 eV both give 3.84; additionally, 150 and 770 eV both give 10.99, 170 and 800 eV both give 6.56, and 200 and 830 eV both give 6.35. For a cross-section curve that varies with energy, such coincidences are not credible and strongly suggest a transcription or data-processing error. Since the shape of the relative TICS, including the local maxima around 350 and 730 eV, is a central result of Sec. 4.3, the table must be re-checked and corrected, or the underlying raw data and fitting procedure must be provided.
  3. [Sec. 4.1, Table I] The proposed mass assignments are internally inconsistent with the listed m/z ranges: (CO2·O)+ is CO3+ with a nominal mass of 60 u, not 62–64 u as given in Table I, while (CO2·O2)+ is CO4+ with a nominal mass of 76 u, not 74–76 u. The text and the Fig. 2 caption use ranges '60–64' and '73–77', which do not match the table. Please reconcile the mass calibration and the assignment of the high-mass features; this is central to the claimed detection of CO3+ and CO4+.
  4. [Sec. 2.2a, Eq. (2)] The text immediately following Eq. (2) states that the equation 'provides absolute values of the integral ionization cross sections', but then says that 'we can only obtain relative values of the ionization cross sections as a function of the anion impact energy'. These statements are directly contradictory. Please clarify the normalization used and, if the data are only relative, remove the absolute-calibration wording or explain why the MCP2 normalization cannot be made absolute.
minor comments (4)
  1. [Sec. 4.3] The phrase 'as derived from the partial ICS shown in Fig. 5' appears to refer to Fig. 4 (the relative intensities of the different cation species); please correct the figure reference.
  2. [Sec. 4.3] The reference to 'see Table II' for the relative TICS values should be to Table III; Table II contains the TEDCS data.
  3. [Sec. 4.3] The text contains the typo 'Similar behavior has been notd'; this should read 'noted'.
  4. [Fig. 4 and Table III] The impact-energy range is stated as 160–900 eV in one place in the text and 150–900 eV in Table III and in Fig. 4; please make the range consistent.

Circularity Check

0 steps flagged · score 1.0 of 10

No significant circularity: the central cross sections are directly measured observables, and the proposed formation mechanism is a post hoc ab initio interpretation rather than a fitted prediction.

full rationale

The paper's central claims are experimental measurements, not outputs of a model fitted to the same data. The absolute TEDCS values in Table II derive from the Beer-Lambert attenuation law (Eq. 1) applied to directly measured transmitted anion intensities versus CO2 pressure; no parameter is fitted to a subset of the data and then renamed as a prediction. The relative TICS values are also explicitly presented as relative, with the paper stating it 'cannot ensure that the primary beam intensity detected by MCP2 corresponds to the actual intensity of this beam in the gas cell,' so no overclaim is made. The theoretical section uses standard ab initio methods (MP2, CCSD(T)) to compute relative energies of possible product channels, and the proposed CO3+/CO4+ mechanism is offered as an interpretation consistent with the detected masses and computed energetics, not as a prediction derived from a circular definition. Self-citations appear for the apparatus description (Refs. 31-33) and for analogies with previous O2- collisions with benzene and N2, but these are methodological and comparative references, not load-bearing reductions of the present result to prior conclusions. The beam-purity concern raised by the presence of O- and O3- in the primary beam is a legitimate experimental-validity question about whether Eq. (1) mixes several detachment channels, but it is not a form of circularity: it concerns systematic error and missing control, not the equivalence of input and output by construction. No equation in the paper defines a predicted quantity in terms of the measured quantity, and no load-bearing argument reduces to a self-citation chain.

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

The central measurement rests on standard experimental assumptions (single-collision, ideal gas, pure beam, detector efficiency) and the theoretical interpretation rests on standard quantum chemistry levels. No parameters were fitted to the data in the theory, and the only proposed new chemical species are the tentatively assigned cation complexes.

assumptions (4)
  • domain assumption Ideal gas behavior and Beer-Lambert single-collision attenuation apply in the gas cell.
    TEDCS are derived from Eq. (1), which assumes exponential attenuation in a uniform gas at pressure P and temperature T with no multiple scattering; the paper states Pmax is chosen to ensure single collision conditions (Section 2.2).
  • domain assumption The measured attenuation is due only to O2- projectiles; residual O- and O3- are removed by the TOF filtering procedure.
    Section 2.1 says the beam 'mainly' contains O2- but also O- and O3-; the paper asserts the extractive pulse tuning acts as a TOF filter, but does not quantify residual contamination.
  • domain assumption MCP1 and MCP2 counting efficiencies are near 100% for both ion beams.
    Section 2.2 states the counting efficiency is about 100%, which is needed for the TICS ratio in Eq. (2), though the paper concedes it cannot ensure the MCP2 signal matches the in-cell beam, which is why TICS are only relative.
  • domain assumption MP2 and CCSD(T) with aug-cc-pVTZ provide accurate relative enthalpies for the proposed mechanisms.
    Section 3 uses these standard quantum chemistry levels to explore PES and assign CO3+/CO4+ formation channels; no error bars or benchmarks against experimental thermochemistry are given.
invented entities (1)
  • CO3+ and CO4+ complexes, written as (CO2·O)+ and (CO2·O2)+
    purpose: Assign the unexpected TOF peaks at m/z 60-64 and 74-76 observed at impact energies above about 500 eV.
    The paper's own mass assignments are labeled tentative, the nominal CO3+ mass does not align cleanly with the listed 62-64 feature, and no external measurement confirms these as the detected species. The ab initio surfaces make them energetically plausible, but that is not independent evidence.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Superoxide anion (O$_{2}\negthinspace^{-}$) collisions with CO$_{2}$ molecules in the energy range 50-950 eV." pith.science (2026). https://pith.science/paper/TZ6L55DP

@misc{pith2026250108107,
  author       = {Pith},
  title        = {Pith review of: Superoxide anion (O$_2\negthinspace^-$) collisions with CO$_2$ molecules in the energy range 50-950 eV},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/TZ6L55DP}},
  note         = {Machine review of arXiv:2501.08107}
}
abstract

A novel gas-phase molecular scattering study is reported for O$_{2}\negthinspace^{-}$ colliding with CO$_{2}$ for impact energies ranging from 50 to 950 eV. The absolute total electron detachment, relative total and partial ionization cross sections have been measured within this energy range and the positive ion yield of those produced during the collisions has been obtained. The primary anionic beam projectile is produced in a pulsed hollow cathode discharge induced plasma, and its interactions with the neutral molecular target occur in a gas cell at a well-known constant pressure. For impact energies above 500 eV high mass (m $>$ 44 u) charged complexes have been detected. With the aid of a theoretical study, using ab initio methods, we propose a mechanism to infer on the formation of these cationic species, which have been assigned as projectile-target stable compounds (CO$_{3}\negthinspace^{+}$ and CO$_{4}\negthinspace^{+}$).

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

39 extracted references · 39 canonical work pages

  1. [1]

    The CO2 Laser

    W. J. Witterman, “The CO2 Laser”, (Springer-Verlag, Berlin 1987)

    work page 1987

  2. [2]

    Omi and K

    T. Omi and K. Numano, Laser Ther. 23, 49 (2014)

    work page 2014

  3. [3]

    W. J. Wiegand and W. L. Nighan, Appl. Phys. Lett. 22 (1973)

    work page 1973

  4. [4]

    A. W. Ehler, J. Appl. Phys. 46 (1975)

    work page 1975

  5. [5]

    Wang, T.-H

    X.-C. Wang, T.-H. Zhang, Y. Sun, Z.-C. Wu, and Y.-T. Zhan, Phys. Plasmas 29, 023505 (2022)

    work page 2022

  6. [6]

    Stierhof, S

    J. Stierhof, S. Kühn, M. Winter, P. Micke, R. Steinbrügge, C. Shah, N. Hell, M. Bissinger, M. Hirsch, R. Ballhausen, M. Lang, C. Gräfe, S. Wipf, R. Cumbee, G. L. Betancourt-Martinez, S. Park, J. Niskanen, M. Chung, F. S. Porter, T. Stöhlker, T. Pfeifer, G. V. Brown, S. Bernitt, P. Hansmann, J. Wilms, J. R. Crespo López-Urrutia, and M. A. Leutenegger, Eur....

    work page 2022

  7. [7]

    W. Wang, R. Snoeckx, X. Zhang, M. S. Cha, and A. Bogaerts, J. Phys. Chem. C 122, 8704 (2018)

    work page 2018

  8. [8]

    E. A. Ainsworth and A. Rogers, Plant, Cell and Environment 30, 258 (2007)

    work page 2007

Show all 39 references
  1. [9]

    A. J. Bloom, M. Burger, J. S. Rubio Asensio, and A. B. Cousins, Science 328, 899 (2010)

    2010

  2. [10]

    M. F. Cotrufo, P. Ineson and Y. Scott, Glob. Change Biol. 4, 43 (1998)

    1998

  3. [11]

    Jenkinson, D, Adams and A.Wild, Nature 351, 304 (1991)

    D. Jenkinson, D, Adams and A.Wild, Nature 351, 304 (1991)

    1991

  4. [12]

    Bolin, J

    B. Bolin, J. Canadell, B. Moore III, I. Noble, and W. Steffen, Science 285, 1849 (1999)

    1999

  5. [13]

    P. M. Dittman, D. Dill and J.L. Dehmer, Chem. Phys. 78, 405 (1983)

    1983

  6. [14]

    K. E. McCulloh, J. Chem. Phys. 59, 4250 (1973)

    1973

  7. [15]

    C. R. Brundle and D. W. Turner, Int. J. Mass Spectrom. Ion Phys. 2, 195 (1969)

    1969

  8. [16]

    A. I. Lozano, A. García-Abenza, F. Blanco, M. Hasan, D. S. Slaughter, T. Weber, R. P. McEachran, R. D. Whit, M. J. Brunger, P. Limão-Vieira, and G. García, J. Phys. Chem. A 126, 6032 (2022)

    2022

  9. [17]

    M. S. Huq, Dissertations, Theses, and Masters Projects, William & Mary, Paper 1539623749 (1984)

    1984

  10. [18]

    K. M. A. Refaey and J. L. Franklin, Int. Mass Spectrom. Ion Phys. 20, 19 (1976)

    1976

  11. [19]

    M. S. Huq, L. D. Doverspike, R. L. Champion, and V. A. Esaulov, J. Phys. B 15, 951 (1982)

    1982

  12. [20]

    V. N. Tuan, V. Esaulov, and J. P. Gauyacq, J. Phys. B 17, L133 (1984)

    1984

  13. [21]

    V. A. Esaulov, J. P. Grouard, R. I. Hall, M. Landau, J. L. Montmagnon, F. Pichou, and C. Schermann, J. Phys. B 17, 1855 (1984)

    1984

  14. [22]

    J. F. Paulson, J. Chem. Phys. 52, 963 (1970)

    1970

  15. [23]

    J. L. Moruzzi and A. V. Phelps, J. Chem. Phys. 45, 4617 (1966)

    1966

  16. [24]

    L. D. Doverspike, B. T. Smith, and R. L. Champion, Phys. Rev. A 22, 393 (1980)

    1980

  17. [25]

    J. B. Greenwood, A. Chutjian, and S. J. Smith, Astrophys. J. 529, 605 (2000)

    2000

  18. [26]

    Hayyan, M

    M. Hayyan, M. A. Hashim and I. M. AlNashef, Chem. Rev. 116, 3029 (2016)

    2016

  19. [27]

    C. M. C. Andrés, J. M. Pérez de la Lastra, C. Andrés Juan, F. J. Plou, and E. Pérez- Lebeña, Int. J. Mol. Sci. 24, 1841 (2023)

    2023

  20. [28]

    S. Jia, S. Ge, X. Fan, K. W. Leong, and J. Ruang, Nanomedicine 16, 759 (2021)

    2021

  21. [29]

    Liu and G

    N. Liu and G. Sun, Ind. Eng. Chem. Res. 50, 5326 (2011)

    2011

  22. [30]

    T. J. Millar, C. Walsh, and T. Field, Chem. Rev. 117, 1765 (2017)

    2017

  23. [31]

    Mendes, C

    M. Mendes, C. Guerra, A. I. Lozano, D. Rojo, J. C. Oller, P. Limão-Vieira, and G. García, Phys. Rev. A 99, 062709 (2019)

    2019

  24. [32]

    Guerra, S

    C. Guerra, S. Kumar, F. Aguilar-Galindo, S. Díaz-Tendero, A. I. Lozano, M. Mendes, P. Limão-Vieira, and G. García, Sci. Rep. 11, 23125 (2021)

    2021

  25. [33]

    Guerra, S

    C. Guerra, S. Kuhmar, F. Aguilar-Galindo, S. Díaz-Tendero, A. I. Lozano, M. Mendes, J. C. Oller, P. Limão-Vieira, and G. García, Int. J. Mol. Sci. 23, 1266 (2022)

    2022

  26. [34]

    Møller, M.S

    C. Møller, M.S. Plesset, Phys. Rev. 46, 618 (1934)

    1934

  27. [35]

    Kendall, T.H

    R.A. Kendall, T.H. Dunning, R.J. Harrison, J. Chem. Phys. 96, 6796 (1992)

    1992

  28. [36]

    D. A. McQuarrie and J. D. Simon, Molecular Thermodynamics, University Science Books (1999)

    1999

  29. [37]

    Čížek, J

    J. Čížek, J. Chem. Phys. 45, 4256 (1966)

    1966

  30. [38]

    Frisch, G

    M.J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, ...

    2016

  31. [39]

    Abu-Haija, E

    O. Abu-Haija, E. Y. Kamber, S. M. Ferguson, and N. Stolterfoht, Phys. Rev. A 72, 042701 (2005)

    2005

Pith tools

Reviewed August 10, 2026 · model on record in the stance chip above.