Interstellar Chemistry of CN Radicals on Ices: The formation of CH3CN and CH3NC and potential connection to acetamide

Joan Enrique-Romero; Thanja Lamberts

REVIEW 4 major objections 5 minor 63 references

Interstellar Chemistry of CN Radicals on Ices: The formation of CH3CN and CH3NC and potential connection to acetamide

T0 review · 4 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash

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Pith's one-line read This paper argues that CN radicals react with methyl radicals on interstellar water and carbon monoxide ices to form methyl cyanide and methyl isocyanide, with the water-ice route governed by methyl diffusion and both routes competing…

desk verdict Solid DFT study with a benchmark and new barriers, but the water-ice 'efficiently' claim is undercut by the paper's own diffusion data. read the letter →

arxiv 2506.08792 v1 pith:W56LS2SC submitted 2025-06-10 astro-ph.GA

Joan Enrique-Romero , Thanja Lamberts This is my paper

classification astro-ph.GA

keywords astrochemistryinterstellaricesCNradicalmethylcyanideisocyanidecouplingquantumtunnellingacetamide

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

Interstellar ices are thought to be the factory floor for complex prebiotic molecules, and this paper tackles a specific step: whether the cyanide radical (CN) sitting on a water or carbon monoxide ice can catch a nearby methyl radical (CH3) to make methyl cyanide (CH3CN) and its isomer methyl isocyanide (CH3NC). Using density functional theory on small ice clusters, the authors find that on water ice the coupling is nearly barrierless, with the rate set by CH3 diffusion until back-diffusion steps in, and on carbon monoxide ice it is barrierless outright. They also trace a competing channel in which hemibonded CN reacts with the water itself, ultimately opening a solid-state route to acetamide, a molecule with a peptide bond. If these results hold, CN radicals on grains are consumed quickly, strengthening the case that nitrile-bearing complex organics form on dust surfaces.

What carries the argument

The load-bearing objects are the hemibonded complex $(\mathrm{H_2O\cdots CN})_\mathrm{hemi}$, a two-centre three-electron bond that pins CN to the water ice surface, and the small ice clusters $(\mathrm{H_2O})_{14}$ and $(\mathrm{CO})_{13}$ used to map reactivity and diffusion. On water, the relevant mechanism is a competition: CH3 must diffuse from a neighbouring binding site to the CN reaction site, and the computed diffusion barriers (average 2.3–3.2 kJ mol$^{-1}$) are comparable to the small coupling barriers (2.8 and 3.1 kJ mol$^{-1}$), with most cyanide-proximal diffusion hops endothermic, so back-diffusion is suppressed. A second mechanism, water-assisted hydrogen transfer (wHt), shuttles protons along chains of two to four water molecules to convert the hemibonded CN into the radical HO–C(=NH)•, with barriers 51.6, 34.1, and 20.7 kJ mol$^{-1}$ and tunnelling crossover temperatures up to roughly 136 K. On CO ice, the coupling of CH3 with either CN or the chemisorbed NC•CO is barrierless, leaving diffusion as the only controlling step.

What would settle it

Measure a CH3 + CN reaction on an interstellar ice analogue: co-deposit or photolytically generate both radicals on an amorphous solid water film near 10 K, warm slowly, and detect products with infrared spectroscopy and temperature-programmed desorption. If CH3CN appears only after diffusion becomes competitive with desorption, or if the CH3NC isomer is absent or far less abundant than CH3CN, the paper's picture of diffusion-controlled, efficient radical coupling with both isomers forming would be contradicted.

Watch

Extended reading notes

Core claim

On its own terms, the paper establishes that a CN radical hemibonded to a water ice cluster reacts with a CH3 radical through both carbon- and nitrogen-attack channels, giving CH3CN and CH3NC with small barriers (2.8 and 3.1 kJ mol$^{-1}$) that are comparable to the barriers for CH3 diffusion across the ice (averaging 2.3–3.2 kJ mol$^{-1}$); because the diffusion trajectories away from CN are mostly endothermic, back-diffusion is suppressed and the coupling is efficient. When CN is instead hydrogen-bonded to water, or physisorbed on a carbon monoxide ice, the coupling is barrierless for both isomers, and on CO ice the chemisorbed intermediate NC•CO likewise adds CH3 without a barrier to form acetyl cyanide. Independently, the paper shows that the hemibonded complex (H2O–CN)hemi can convert, via water-assisted hydrogen transfer over chains of two to four water molecules, into the radical HO•CNH, with activation barriers of 51.6, 34.1, and 20.7 kJ mol$^{-1}$ that can be overcome by quantum tunnelling; HO•CNH then reacts with CH3 (barriers 1.2–3.1 kJ mol$^{-1}$) to give acetimidic acid, which isomerizes to acetamide through a water-assisted tautomerization whose barrier (20.0 kJ mol$^{-1}$ in the lower binding mode) is tunnelling-accessible. The overall conclusion is that CN radicals on interstellar grains are far too reactive to persist, and that radical coupling on ices is a viable formation route for both CH3CN and CH3NC.

Load-bearing premise

The conclusion that CH3 stays at the reactive site long enough for efficient coupling rests on diffusion barriers computed on a single (H2O)14 cluster, whose transition states are so flat (imaginary frequencies of 10–90 cm$^{-1}$) that the harmonic estimates may be unreliable; if those barriers are artifacts of the cluster or the method, the claim that back-diffusion is suppressed and that the water-ice route is efficient is unsupported.

Editorial extensions

If this is right

CN radicals on interstellar grains are unlikely to survive: they are converted to HCN, HNC, CH3CN, CH3NC, or HO•CNH depending on which reaction partners are available.
On water ice, CH3CN and CH3NC formation is controlled by CH3 diffusion and the local binding landscape, so the efficiency is not a single number but depends on ice structure and temperature.
On CO-dominated ices, CH3 + CN coupling is barrierless, and CH3 + NC•CO barrierlessly yields CH3C(O)CN, so CO ice chemistry produces acetyl cyanide as an additional product.
The water-assisted route from hemibonded CN to HO•CNH, then CH3 addition to acetimidic acid and tautomerization, provides a solid-state path to acetamide whose rate-limiting steps are tunnelling-driven and strongly dependent on the local water network.
Standard astrochemical recipes that set diffusion barriers at a fixed fraction (0.3–0.5) of the binding energy may underestimate the mobility of radicals like CH3 on water ice.

Reading between the lines

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

If CH3NC forms alongside CH3CN on grains, the isomer ratio observed in the gas phase could encode information about the ice surface (water vs CO dominated) and the diffusion history, which could be tested by mapping CH3NC/CH3CN column density ratios across different star-forming environments.
The strong sensitivity of the tunnelling steps to the local water chain length suggests that a mixed H2O/CO ice, which changes the effective hydrogen-bond network, could switch the network between the CH3CN/CH3NC channel and the acetamide channel; experiments on layered versus mixed ices would test this switching.
Because CN is so quickly consumed on grains, gas-phase detections of CN may require a continuous supply from non-thermal desorption or from gas-phase chemistry rather than a reservoir of CN frozen on grains, which would revise how CN abundances are interpreted in astrochemical models.
The proposed acetamide sequence implies a chemical family relationship: regions rich in CH3CN should also show enhanced acetamide and possibly HOCN/HNCO if the same CN reservoir feeds all these products; correlating these species in interferometric maps could provide an observational fingerprint of the solid-state network.

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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

The paper is a competent DFT study that extends the authors' previous work on CN radical chemistry on interstellar ices. The genuinely new results are the explicit CH3 diffusion barriers on a (H2O)14 cluster with and without a hemibonded CN, the barrierless CH3 + CN and CH3 + NCCO couplings on CO ice, and the water-assisted acetimidic acid-to-acetamide isomerization barriers. The benchmark against CCSD(T)-F12, CASPT2, and NEVPT2 gives real credibility to the method choice, and the deposited Zenodo data is a plus.

The soft spot is the abstract's 'efficiently' for CH3CN/CH3NC formation on water ice. The stress-test note is correct: their own numbers put the lowest CH3 escape barrier at 1.1 kJ/mol while the reaction barriers are 2.8 and 3.1 kJ/mol. At 10 K, that is roughly 10^9 in favor of escape. The authors' argument that endothermic escape steps suppress back-diffusion doesn't work—the forward barrier, not the reaction energy, controls the escape rate, and an endothermic escape just makes the return step even faster. The paper does warn that the diffusion TS have low imaginary frequencies (10–90 cm-1), but that caution appears in Section 3.2, not in the abstract or conclusions. No rate constants or tunneling probabilities are reported; crossover temperatures alone don't establish efficiency. So the central claim on water ice is unsupported by the static energetics.

That said, the paper still has value. The CO-ice pathways are barrierless and more robust, and the acetamide route via acetimidic acid is an interesting proposal worth testing. The authors are explicit that kinetic modeling is future work, which is honest, but they should soften the abstract until that modeling is done.

My recommendation: send it to peer review. A referee should ask for either a simple kinetic model (TST with tunneling corrections) or a revised abstract that says 'energetically favorable but limited by competition with back-diffusion.' The manual preparation of a few reactant geometries should also be reported more prominently, not just as footnotes.

Referee Report

4 major / 5 minor

Summary. This manuscript presents a density functional theory study (BHandHLYP-D4, with RSCAN-D3(BJ) for one channel, benchmarked against CCSD(T)-F12, CASPT2, and NEVPT2) of the reactions of CN radicals with CH3 radicals on water and carbon monoxide ice cluster models. The authors map potential energy surfaces for C–C and C–N coupling to form CH3CN and CH3NC, compute diffusion barriers for CH3 on a (H2O)14 cluster with and without a hemibonded CN, explore water-assisted H-transfer converting hemibonded CN to HO•CNH, and propose a pathway to acetamide via acetimidic acid followed by water-catalyzed tautomerization. The main claims are that hemibonded CN on water reacts with CH3 through small barriers (2.8 and 3.1 kJ/mol), that hydrogen-bonded CN on water and all CN binding modes on CO ice react barrierlessly, that the reactions compete with CH3 back-diffusion, and that the acetamide route requires quantum tunneling.

Significance. If quantitatively supported, the manuscript would provide a concrete solid-state formation route to methyl cyanide and methyl isocyanide and a new, chemically explicit pathway to acetamide, connecting CN chemistry on ices to prebiotic molecules. The benchmark against high-level multireference methods and the public deposition of data in Zenodo are strengths. However, the abstract's central claim that CN reacts with CH3 on water ices 'efficiently' is a kinetic statement that is not backed by rate constants, tunneling probabilities, or a kinetic model; the static barrier heights alone do not establish efficiency at interstellar temperatures. The paper is useful as a careful PES mapping, but its quantitative conclusions need substantial revision or softening.

major comments (4)

[§3.2, Table 3 vs. §3.1, Table 2] The conclusion that back-diffusion is 'effectively suppressed' is not supported by the reported numbers. The ZPVE-corrected barrier for CH3 hopping from the reactive site to BS1 is 1.1 kJ/mol (Table 3), while the reaction barriers are 2.8 kJ/mol (CH3CN) and 3.1 kJ/mol (CH3NC) (Table 2). At 10 K, a simple transition-state-theory estimate gives an escape-to-reaction rate ratio of roughly exp((2.8-1.1)/(R·10 K)) ≈ 10^9, so the methyl radical will leave the reactive site far more often than it reacts. The endothermicity of three of the four escape hops does not suppress escape; the reverse hops are then even faster, so the radical shuttles among binding sites rather than remaining at the reactive one. The statement 'we expect back-diffusion to be effectively suppressed' (end of §3.2) is therefore contradicted by the presented energetics, and the abstract's 'efficiently' is unsupported without a kinetic model.
[§3.1, Table 2] The reaction barriers for hemibonded CN + CH3 (2.8 and 3.1 kJ/mol) correspond to roughly 340-370 K. At typical interstellar grain temperatures of about 10 K, the thermal rate is negligible unless quantum tunneling is efficient. The manuscript reports imaginary frequencies (117 and 100 cm^-1) for these transition states but does not compute tunneling probabilities, crossover temperatures, or rate constants for these reactions. The claim that these reactions proceed 'efficiently' therefore requires either explicit tunneling calculations or a temperature-qualified statement. The CH3NC barrier is also strongly method-sensitive: Table 1 shows a spread of 2.8-77.2 kJ/mol across DFT functionals for the analogous reaction on a water trimer, so the reported 3.1 kJ/mol value carries considerable uncertainty even apart from kinetics.
[§3.2, Table 3] The diffusion barriers are computed on a single (H2O)14 cluster, and the transition states have harmonic imaginary frequencies as low as 10-90 cm^-1. The authors appropriately caution that these TS 'should be interpreted with care,' yet the back-diffusion argument rests on the heights of these very barriers. With such low imaginary frequencies, anharmonic corrections or changes in cluster size could easily reorder the barriers relative to the 2.8-3.1 kJ/mol reaction barriers. In particular, the 1.1 kJ/mol BS1 escape barrier might shift above or below the reaction barrier, which would flip the qualitative conclusion. A robustness check with a different cluster size or an alternative treatment of the low-frequency modes is needed before drawing the quantitative back-diffusion inference.
[§4, abstract] The proposed acetamide route (HO•CNH + CH3 → acetimidic acid → acetamide) is presented with barrier heights and crossover temperatures but without rate constants or tunneling rates. The abstract states that acetimidic acid 'can only isomerize into acetamide through a sizable barrier thanks to quantum tunnelling,' but this is not demonstrated. Crossover temperatures (58 and 134 K for the two binding modes) indicate that tunneling may be relevant, but a full tunneling rate calculation is needed to claim that the reaction can proceed by tunneling under interstellar conditions. As written, the 'potential connection to acetamide' in the title remains an unquantified hypothesis.

minor comments (5)

[Abstract] The bullet symbols preceding CN and CH3 are formatting artifacts and should be removed for clarity.
[§3.1] The heading 'Water-assisted COM formation' uses the abbreviation COM without defining it; presumably it stands for 'complex organic molecule.'
[Table 2] The reaction energy for CH3CN formation on water (-495.1 kJ/mol) is surprisingly large; please verify that this value is not a typo and clearly define the reference state used for reaction energies.
[§4] The sentence 'the activation energy for the formation of either CH3CN and CH3NC are as low as the diffusion barriers' has a grammatical error; it should read 'either CH3CN or CH3NC.'
[References] The page field for Goesmann et al. (2015) reads '2.689,' which appears to be a malformed article number; please correct.

Circularity Check

0 steps flagged · score 1.0 of 10

No significant circularity: the reaction and diffusion barriers are computed from DFT benchmarked against external high-level references, and prior self-cited work supplies input premises rather than the derived result.

full rationale

The paper's central claims are the barrier heights and diffusional competition for CH3 + CN on water and CO ices. These are obtained from direct DFT calculations, and the functional choice is benchmarked against independent high-level references: CCSD(T)-F12, CASPT2, and NEVPT2 (Sect. 2, Table 1). No fitted parameter is renamed as a prediction; in particular, the CH3CN and CH3NC formation barriers (2.8 and 3.1 kJ/mol on water, Table 2) and the CH3 diffusion barriers (Table 3) are computed, not imposed. The only self-citations to Enrique-Romero & Lamberts (2024) establish input premises: the hemibonded binding mode of CN on water, the (CO)13 cluster model, and prior CN + H reactivity. These are load-bearing in the sense that the paper starts from them, but they are not the result being derived; the new result is the radical-radical coupling efficiency, which is computed here and is not equivalent to those premises by construction. The statement that back-diffusion is 'effectively suppressed' is an inference from endothermic diffusion steps (Sect. 3.2), not a fitted or self-cited quantity. Whether that inference is quantitatively sound—for example, the lowest escape barrier of 1.1 kJ/mol being below the reaction barrier of 2.8 kJ/mol—is a correctness or robustness concern, not circularity. The authors explicitly caution that the diffusion transition states have very low harmonic imaginary frequencies (10–90 cm-1) and should be interpreted with care; this limitation is flagged in the manuscript and does not make the derivation circular. Overall, the central derivation is self-contained against external benchmarks, with only a minor non-circular reliance on the authors' prior work for input structures and premises.

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

The paper introduces no new particles, forces, or conserved quantities. The input assumptions are cluster representativeness, DFT reliability after benchmarking, and crossover-temperature-based tunnelling inference. There are no numbers fitted to experimental data; all barriers are computed outputs.

assumptions (4)

domain assumption Small cluster models ((H2O)14, (CO)13, (H2O)3) are representative of amorphous interstellar ice surfaces.
All barriers, binding modes, and diffusion energetics are derived from these finite clusters; no amorphous surface sampling or embedding is used. Invoked throughout Sect. 3.
domain assumption DFT functionals BHandHLYP-D4 and RSCAN-D3(BJ) give reliable barrier heights for the reactions studied.
The benchmark (Table 1) validates selected functionals against CCSD(T)-F12, CASPT2, and NEVPT2 for a subset of reactions, but DFT remains an approximation for all other points and no uncertainty is propagated.
domain assumption Crossover temperatures indicate that quantum tunnelling overcomes the reported barriers under interstellar conditions.
The wHt and AAc to Am conclusions rely on crossover temperatures (e.g., 71-134 K) as tunnelling indicators; no actual tunnelling rate constants or transmission coefficients are computed. Invoked in Sect. 3.1 and Sect. 4.
domain assumption Harmonic vibrational analysis is adequate for zero-point corrections of diffusion transition states.
The authors caution that diffusion TS have very low imaginary frequencies, 10-90 cm-1, and that ZPVE may be overestimated because van der Waals interactions are anharmonic (Sect. 3.2).

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Cite this review

Pith. "Pith review of Interstellar Chemistry of CN Radicals on Ices: The formation of CH3CN and CH3NC and potential connection to acetamide." pith.science (2026). https://pith.science/paper/W56LS2SC

@misc{pith2026250608792,
  author       = {Pith},
  title        = {Pith review of: Interstellar Chemistry of CN Radicals on Ices: The formation of CH3CN and CH3NC and potential connection to acetamide},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/W56LS2SC}},
  note         = {Machine review of arXiv:2506.08792}
}

read the original abstract

Context. Among the most significant chemical functional groups of interstellar molecules are the class of nitriles, which are proposed as key prebiotic molecules due to their chemical connection to the peptide bond after hydrolysis. CN radicals, the simplest representative of this group, have been shown to exhibit strong interactions with interstellar water ices, potentially impacting their reactivity with other radicals nearby. Aims. This study explores (a) whether CN and CH3 radicals can readily react to form methyl cyanide (CH3CN) and its isomer methyl isocyanide (CH3NC); and (b) the feasibility of the reaction (CN...H2O)hemi -> C(OH)=NH and its potential role in the formation of acetamide. Methods. Following a benchmark, density functional theory was employed to map the potential energy surfaces of these chemical processes, focusing on their reactivity on water and carbon monoxide ices. Results. The results show that CN reacts with CH3 radicals on water ices, forming CH3CN and CH3NC efficiently. However, these reactions are driven by diffusion of CH3 towards the reactive site and subsequently compete with back-diffusion of CH3 from that site. The formation of the radical intermediate C(OH)=NH on water ice requires quantum tunnelling and assuming that acetimidic acid forms via CH3 + C(OH)=NH -> CH3C(OH)=NH, it can also only isomerize into acetamide through a sizable barrier thanks to quantum tunnelling. Both quantum tunnelling-driven reactions are highly dependent on the local structure of the water ice. Finally, radical coupling reactions on carbon monoxide ices are found to be barrierless for all cases and again, both the cyanide and the isocyanide are formed. Conclusions. This work reinforces the conclusion that CN radicals on interstellar grain surfaces are highly reactive and unlikely to persist unaltered.

Figures

Figures reproduced from arXiv: 2506.08792 by the authors.

**Figure 1.** Snapshots of the potential energy surface stationary points for the formation of (a) CH3CN and (b) CH3NC on the (H2O)14 ice cluster, where the •CN radical is initially hemibonded to the ice. Distances in Å. Atoms relevant to the reaction are highlighted using a ball-and-stick representation. Atom colour code is: red for O, blue for N, grey for C and white for H. (a) First step, water-assisted H-transfer (wHt(4)) (b)… view at source ↗

**Figure 2.** Snapshots of the potential energy surface stationary points for (a) the (H2O – •CN)hemi → HO•C––NH reaction (wHt(4)), and (b) a second step where acetimidic acid is formed via •CH3 + HO•C––NH → CH3C(OH)NH (i) and an alternative path leading to CH4 + HNCO through a direct H-transfer reaction. Distances are provided in Å. Atoms relevant to the reaction are highlighted using a ball-and-stick representation. Atom colour… view at source ↗

**Figure 3.** Snapshots of the potential energy surface stationary points to form cyanic acid (HOCN) from the direct H-abstraction reaction HO•CNH + CH3 on the (H2O)14 cluster. The reactants geometry was prepared manually to mimic that in 2(b). Distances in Å. Atoms relevant to the reaction are highlighted using a ball-and-stick representation. Atom colour code is: red for O, blue for N, grey for C and white for H [PITH_FULL_IM… view at source ↗

Figures from the paper (3 more)

**Figure 4.** Figure 4: Diffusion of •CH3 from the initial binding site (BS0) to the neighbouring binding site BS3 for two scenarios: a) •CN – (H2O)14 and the bare ice b) (H2O)14. The arrows indicate the motion the CH3 radical follows when it hops to BS3. The initial BS0 geometry in the left…

**Figure 5.** Figure 5: Snapshots of the potential energy surface stationary points for the acetimidic acid to acetamide isomerisation. The upper panel, a), corresponds to the high barrier isomerisation reaction case, while the lower panel, b), to the lower barrier one. Distances are provide…

**Figure 6.** Figure 6: Summary of the reactions studied in this work between •CH3 + •CN on water and carbon monoxide ice surfaces. The first line indicates the possible outcomes of diffusive chemistry, while the second indicates the products after the reaction with one of the ice molecules …

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Works this paper leans on

63 extracted references · 58 canonical work pages

[1]

J., et al

Altwegg, K., Balsiger, H., Berthelier, J. J., et al. 2017, MNRAS, 469, S130

2017
[2]

Altwegg, K., Balsiger, H., & Fuselier, S. A. 2019, ARA&A, 57, 113

work page 2019
[3]

2001, JCP, 114, 10252

Angeli, C., Cimiraglia, R., Evangelisti, S., Leininger, T., & Malrieu, J.-P. 2001, JCP, 114, 10252

work page 2001
[4]

2007, Theor

Angeli, C., Pastore, M., & Cimiraglia, R. 2007, Theor. Chem. Acc., 117, 743 Ásgeirsson, V ., Birgisson, B. O., Bjornsson, R., et al. 2021, J. Chem. Theory Comput., 17, 4929

work page 2007
[5]

F., & Lindh, R

Battaglia, S., Galván, I. F., & Lindh, R. 2023, in Theoretical and Computational Photochemistry (Elsevier), 135–162

work page 2023
[6]

Becke, A. D. 1993, JCP, 98, 5648

work page 1993
[7]

A., Garrod, R

Belloche, A., Meshcheryakov, A. A., Garrod, R. T., et al. 2017, A&A, 601, A49

work page 2017
[8]

B., Öberg, K

Bergner, J. B., Öberg, K. I., Garrod, R. T., & Graninger, D. M. 2017, ApJ, 841, 120

work page 2017

Show all 63 references

[9]

2022, A&A, 662, A103

Bianchi, E., Ceccarelli, C., Codella, C., et al. 2022, A&A, 662, A103

2022
[10]

Boogert, A. C. A., Gerakines, P. A., & Whittet, D. C. B. 2015, ARA&A, 53, 541

2015
[11]

M., V ogt-Geisse, S., Bovino, S., & Grassi, T

Bovolenta, G. M., V ogt-Geisse, S., Bovino, S., & Grassi, T. 2022, ApJS, 262, 17

2022
[12]

M., Fedoseev, G., & Linnartz, H

Bulak, M., Paardekooper, D. M., Fedoseev, G., & Linnartz, H. 2021, A&A, 647, A82

2021
[13]

2017, JCP, 147

Caldeweyher, E., Bannwarth, C., & Grimme, S. 2017, JCP, 147

2017
[14]

I., & Rajappan, M

Canta, A., Öberg, K. I., & Rajappan, M. 2023, ApJ, 953, 81

2023
[15]

2023, in ASPC, V ol

Ceccarelli, C., Codella, C., Balucani, N., et al. 2023, in ASPC, V ol. 534, Pro- tostars and Planets VII, ed. S. Inutsuka, Y . Aikawa, T. Muto, K. Tomida, & M. Tamura, 379

2023
[16]

& Werner, H.-J

Celani, P. & Werner, H.-J. 2000, JCP, 112, 5546

2000
[17]

J., Jäger, C., Santos, J

Chuang, K. J., Jäger, C., Santos, J. C., & Henning, T. 2024, A&A, 687, A7

2024
[18]

M., Beltrán, M

Colzi, L., Rivilla, V . M., Beltrán, M. T., et al. 2021, A&A, 653, A129

2021
[19]

M., Linnartz, H., & Ioppolo, S

Cuppen, H. M., Linnartz, H., & Ioppolo, S. 2024, ARA&A, 62, 243

2024
[20]

B., de Marcellus, P., et al

Danger, G., Bossa, J. B., de Marcellus, P., et al. 2011, A&A, 525, A30

2011
[21]

D., V olosatova, A

Drabkin, V . D., V olosatova, A. D., & Feldman, V . I. 2023, MNRAS, 518, 1744

2023
[22]

2021, Frontiers in Astronomy and Space Sciences, 8, 24

Duflot, D., Toubin, C., & Monnerville, M. 2021, Frontiers in Astronomy and Space Sciences, 8, 24

2021
[23]

& Lamberts, T

Enrique-Romero, J. & Lamberts, T. 2024, JCPL, 15, 7799

2024
[24]

2020, ApJ, 904, 11

Ferrero, S., Zamirri, L., Ceccarelli, C., et al. 2020, ApJ, 904, 11

2020
[25]

M., et al

Frigge, R., Zhu, C., Turner, A. M., et al. 2018, ApJ, 862, 84

2018
[26]

Garrod, R. T. & Herbst, E. 2006, A&A, 457, 927

2006
[27]

T., Widicus Weaver, S

Garrod, R. T., Widicus Weaver, S. L., & Herbst, E. 2008, ApJ, 682, 283

2008
[28]

2023, MNRAS, 526, 4535

Giani, L., Ceccarelli, C., Mancini, L., et al. 2023, MNRAS, 526, 4535

2023
[29]

H., et al

Goesmann, F., Rosenbauer, H., Bredehöft, J. H., et al. 2015, Science, 349, 2.689

2015
[30]

J., Fried, L

Goldman, N., Reed, E. J., Fried, L. E., William Kuo, I. F., & Maiti, A. 2010, Nature Chemistry, 2, 949

2010
[31]

T., Ilyushin, V ., & Ziurys, L

Halfen, D. T., Ilyushin, V ., & Ziurys, L. M. 2011, ApJ, 743, 60

2011
[32]

& Rappoport, D

Hellweg, A. & Rappoport, D. 2015, PCCP, 17, 1010 Article number, page 8 of 10

2015
[33]

2017, ApJ, 154, 38

Holdship, J., Viti, S., Jiménez-Serra, I., Makrymallis, A., & Priestley, F. 2017, ApJ, 154, 38

2017
[34]

J., Remijan, A

Hollis, J., Lovas, F. J., Remijan, A. J., et al. 2006, ApJ, 643, L25

2006
[35]

L., Moore, M

Hudson, R. L., Moore, M. H., Dworkin, J. P., Martin, M. P., & Pozun, Z. D. 2008, Astrobiology, 8, 771

2008
[36]

D., Walsh, C., Booth, A

Ilee, J. D., Walsh, C., Booth, A. S., et al. 2021, ApJS, 257, 9

2021
[37]

B., & Werner, H.-J

Knizia, G., Adler, T. B., & Werner, H.-J. 2009, JCP, 130, 054104

2009
[38]

N., Kolb, F

Lamberts, T., Markmeyer, M. N., Kolb, F. J., & Kästner, J. 2019, ACS Earth Space Chem., 3, 958 Le Roy, L., Altwegg, K., Balsiger, H., et al. 2015, A&A, 583, A1 Li Manni, G., Fdez. Galva’an, I., Alavi, A., et al. 2023, J. Chem. Theory Com- put., 19, 6933

2019
[39]

Ligterink, N. F. W., Ahmadi, A., Luitel, B., et al. 2022, ACS Earth Space Chem., 6, 455

2022
[40]

Ligterink, N. F. W., Terwisscha van Scheltinga, J., Taquet, V ., et al. 2018, MN- RAS, 480, 3628

2018
[41]

A., Cleeves, L

Loomis, R. A., Cleeves, L. I., Öberg, K. I., et al. 2018, ApJ, 859, 131

2018
[42]

2024, A&A, 691, A83

Mancini, L., Valença Ferreira de Aragão, E., Pirani, F., et al. 2024, A&A, 691, A83

2024
[43]

K., Rocha, W

McClure, M. K., Rocha, W. R. M., Pontoppidan, K. M., et al. 2023, Nat. Astron., 7, 431

2023
[44]

J., et al

McElroy, D., Walsh, C., Markwick, A. J., et al. 2013, A&A, 550, A36 Megías, A., Jiménez-Serra, I., Martín-Pintado, J., et al. 2023, MNRAS, 519, 1601

2013
[45]

D., van Gelder, M

Nazari, P., Meijerhof, J. D., van Gelder, M. L., et al. 2022, A&A, 668, A109

2022
[46]

Nazari, P., Rocha, W. R. M., Rubinstein, A. E., et al. 2024, A&A, 686, A71

2024
[47]

L., van Dishoeck, E

Nazari, P., van Gelder, M. L., van Dishoeck, E. F., et al. 2021, A&A, 650, A150

2021
[48]

2022, WIREs Comput

Neese, F. 2022, WIREs Comput. Mol. Sci., 12

2022
[49]

2020, JCP, 152, 224108 Öberg, K

Neese, F., Wennmohs, F., Becker, U., & Riplinger, C. 2020, JCP, 152, 224108 Öberg, K. I., Guzmán, V . V ., Furuya, K., et al. 2015, Nature, 520, 198

2020
[50]

& Herbst, E

Quan, D. & Herbst, E. 2007, A&A, 474, 521

2007
[51]

T., Enrique-Romero, J., & Lamberts, T

Raaphorst, M. T., Enrique-Romero, J., & Lamberts, T. 2025, ACS Earth Space Chem

2025
[52]

2014, ApJ, 793, 32

Redondo, P., Barrientos, C., & Largo, A. 2014, ApJ, 793, 32

2014
[53]

2018, ACS Earth Space Chem., 2, 720

Rimola, A., Skouteris, D., Balucani, N., et al. 2018, ACS Earth Space Chem., 2, 720

2018
[54]

M., Sanz-Novo, M., Jiménez-Serra, I., et al

Rivilla, V . M., Sanz-Novo, M., Jiménez-Serra, I., et al. 2023, ApJ, 953, L20

2023
[55]

R., Sun, Q., Chan, G

Sayfutyarova, E. R., Sun, Q., Chan, G. K.-L., & Knizia, G. 2017, J Chem Theory Comput., 13, 4063

2017
[56]

2024, MNRAS, 533, 4104

Scibelli, S., Shirley, Y ., Megías, A., & Jiménez-Serra, I. 2024, MNRAS, 533, 4104

2024
[57]

M., Rani, N., Vera, S., & V ogt-Geisse, S

Silva-Vera, G., Bovolenta, G. M., Rani, N., Vera, S., & V ogt-Geisse, S. 2024, ACS Earth Space Chem., 8, 1480 V olosatova, A. D., Lukianova, M. A., Zasimov, P. V ., & Feldman, V . I. 2021, PCCP, 23, 18449

2024
[58]

C., Herbst, E., et al

Wakelam, V ., Loison, J. C., Herbst, E., et al. 2015, ApJS, 217, 20

2015
[59]

1996, Mol

Werner, H.-J. 1996, Mol. Phys., 89, 645

1996
[60]

J., Knizia, G., Manby, F

Werner, H.-J., Knowles, P. J., Knizia, G., Manby, F. R., & Schütz, M. 2012, Wiley Interdiscip. Rev. Comput. Mol. Sci., 2, 242

2012
[61]

J., Manby, F

Werner, H.-J., Knowles, P. J., Manby, F. R., et al. 2020, JCP, 152, 144107

2020
[62]

2021, ApJ, 910, 20

Yang, Y .-L., Sakai, N., Zhang, Y ., et al. 2021, ApJ, 910, 20

2021
[63]

M., Jiménez-Serra, I., et al

Zeng, S., Rivilla, V . M., Jiménez-Serra, I., et al. 2023, MNRAS, 523, 1448 Article number, page 9 of 10 A&A proofs: manuscript no. aa55360-25 Appendix A: Benchmark This section presents the structures used in our benchmark study; corresponding energetic data are available in ...

2023

Pith tools

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

[1] [1]

J., et al

Altwegg, K., Balsiger, H., Berthelier, J. J., et al. 2017, MNRAS, 469, S130

2017

[2] [2]

Altwegg, K., Balsiger, H., & Fuselier, S. A. 2019, ARA&A, 57, 113

work page 2019

[3] [3]

2001, JCP, 114, 10252

Angeli, C., Cimiraglia, R., Evangelisti, S., Leininger, T., & Malrieu, J.-P. 2001, JCP, 114, 10252

work page 2001

[4] [4]

2007, Theor

Angeli, C., Pastore, M., & Cimiraglia, R. 2007, Theor. Chem. Acc., 117, 743 Ásgeirsson, V ., Birgisson, B. O., Bjornsson, R., et al. 2021, J. Chem. Theory Comput., 17, 4929

work page 2007

[5] [5]

F., & Lindh, R

Battaglia, S., Galván, I. F., & Lindh, R. 2023, in Theoretical and Computational Photochemistry (Elsevier), 135–162

work page 2023

[6] [6]

Becke, A. D. 1993, JCP, 98, 5648

work page 1993

[7] [7]

A., Garrod, R

Belloche, A., Meshcheryakov, A. A., Garrod, R. T., et al. 2017, A&A, 601, A49

work page 2017

[8] [8]

B., Öberg, K

Bergner, J. B., Öberg, K. I., Garrod, R. T., & Graninger, D. M. 2017, ApJ, 841, 120

work page 2017