UV irradiation of ethanol-containing interstellar ice analogs: Photostability in CH3CH2OH:CO mixtures

E. F. van Dishoeck; J. A. DeVine; J. Terwisscha van Scheltinga; K.-J. Chuang; S. Ioppolo; T. Lamberts

arxiv: 2510.27422 · v1 · submitted 2025-10-31 · 🌌 astro-ph.GA

UV irradiation of ethanol-containing interstellar ice analogs: Photostability in CH3CH2OH:CO mixtures

J. A. DeVine , J. Terwisscha van Scheltinga , S. Ioppolo , K.-J. Chuang , E. F. van Dishoeck , T. Lamberts This is my paper

Pith reviewed 2026-05-18 03:21 UTC · model grok-4.3

classification 🌌 astro-ph.GA

keywords ethanolinterstellar icesUV photochemistryphotodestruction cross sectionCO mixturesice analogsradiative transfer

0 comments

The pith

CO stabilizes ethanol against UV photodestruction in interstellar ice mixtures.

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

The paper shows that adding CO to ethanol ices reduces the rate at which UV light destroys the ethanol molecules. This stabilization becomes stronger in mixtures where ethanol is highly diluted in CO, which matches the dilute compositions expected in actual interstellar ices. The authors track the solid ice with infrared spectroscopy while a new radiative-transfer model corrects for the fact that both ethanol and its photoproducts keep absorbing UV photons as irradiation continues. They report a photodestruction cross section of roughly 1.6 times 10 to the minus 17 square centimeters per photon once the effective fluence is properly accounted for. The result highlights that the balance between destruction and the formation of new species depends strongly on the initial ice composition.

Core claim

In UV-irradiated ethanol-CO ice mixtures at 16 K, carbon monoxide exerts a stabilizing effect on ethanol. Photodestruction cross sections decrease as the CO fraction increases, reaching an estimated value of approximately 1.6E-17 cm2 per photon for highly dilute ethanol:CO ratios representative of astronomical ices, after the effective absorbed UV fluence is corrected using a radiative-transfer model that incorporates evolving absorption by ethanol and its photoproducts.

What carries the argument

Composition-dependent photodestruction cross section of ethanol, obtained by applying a radiative-transfer model that tracks how ethanol and its photoproducts absorb UV photons throughout irradiation.

Load-bearing premise

The radiative-transfer model correctly calculates the changing number of UV photons actually absorbed by ethanol as the ice composition and photoproducts evolve.

What would settle it

Laboratory measurement of ethanol loss rates in a 1:10 or more dilute ethanol-CO ice at 16 K, compared directly to the model's predicted destruction curve without any fluence correction applied.

read the original abstract

Ethanol (CH3CH2OH) has been detected in interstellar ices within regions associated with the early stages of star and planet formation. Its solid-phase pathways can lead to diverse conditions that can significantly influence its photostability and -chemistry. Laboratory studies have explored the effects of energetic processing on pure ethanol ices, there is a gap in understanding how ethanol behaves in astrophysically relevant mixed ices. This proof-of-principle study aims to quantify how the ice composition influences the photostability of ethanol mixed with CO, from both physical and chemical perspectives. It also seeks to highlight the importance of balancing constructive and destructive processes. Mixtures with ethanol to CO ratios ranging from 1:0 to 1:11 are exposed to UV irradiation from a microwave discharge H lamp under UHV conditions, at 16 K. The evolution of the solid phase is tracked using reflection-absorption infrared spectroscopy, and changes in the gas phase are monitored with a quadrupole mass spectrometer. Temperature-programmed desorption experiments aid in the identification of infrared spectral features. A radiative-transfer model has been developed to account for the influence of ice composition on the effective photon flux. The model reveals that, during later stages of irradiation, photoproducts play a significant role in the absorbing of incident photons, highlighting the complex cascade of processes initiated by single-photon absorption in ethanol-containing ices. By evaluating photodestruction cross sections as a function of the initial ice composition, we found that CO exerts a stabilizing effect on ethanol. For highly dilute ethanol:CO mixtures, representative of astronomical ices, the photodestruction cross section of ethanol is estimated to ~1.6E-17 cm2/photon after correcting for the effective absorbed UV fluence of the studied interstellar ice analogs.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

CO appears to stabilize ethanol in mixed ices with a corrected cross section of ~1.6E-17 cm2/photon in dilute cases, but the result depends on their radiative transfer model for effective fluence.

read the letter

The key point here is that CO in the ice mixture reduces the photodestruction of ethanol, with the cross section dropping to around 1.6 x 10^{-17} cm² per photon in highly dilute cases once they correct for the effective fluence. They do a good job filling the gap left by pure-ice studies. The experiments cover a range of ethanol:CO ratios, irradiate at 16 K with a microwave discharge H lamp, and monitor both the solid with reflection-absorption infrared spectroscopy and the gas with a quadrupole mass spectrometer. Temperature-programmed desorption helps with identifying the IR features. They also built a radiative-transfer model to handle how the ice composition and accumulating photoproducts change the absorbed photon flux over time. That model shows photoproducts become important absorbers later on, which is a reasonable point to make. The main soft spot is the model itself. The headline numbers for composition-dependent cross sections only come after applying this correction. If the treatment of time-dependent absorption or the UV properties of the photoproducts isn't accurate, the apparent stabilizing effect of CO could be exaggerated or even created by the correction step. It would help to see how the model performs on pure ethanol ices, where independent cross section values exist for comparison. The abstract doesn't give those checks, so that's where a referee should look closely. This paper is for people who build astrochemical models of organic molecules in interstellar ices. Anyone working on photostability during early star and planet formation stages could use the new mixture data as input, provided they are comfortable with the fluence correction. I would recommend sending it to peer review. The experimental design is straightforward and relevant, and the attempt to quantify the composition effect is worth referee time even if revisions are needed on the modeling side.

Referee Report

2 major / 2 minor

Summary. The manuscript reports UV irradiation experiments at 16 K on ethanol:CO ice mixtures (ratios from 1:0 to 1:11) under UHV conditions. Reflection-absorption infrared spectroscopy tracks solid-phase evolution while a quadrupole mass spectrometer monitors the gas phase; temperature-programmed desorption aids spectral assignments. A radiative-transfer model is developed to correct observed IR decay rates for the time-dependent effective UV fluence absorbed by both ethanol and accumulating photoproducts. From the corrected rates the authors derive composition-dependent photodestruction cross sections and conclude that CO exerts a stabilizing effect, yielding an estimated cross section of ~1.6 × 10^{-17} cm²/photon for highly dilute mixtures representative of astronomical ices.

Significance. If the fluence-correction model is shown to be robust, the work supplies quantitative laboratory constraints on how matrix composition modulates ethanol photostability in interstellar ices. Such data are directly usable in astrochemical networks that track the survival of complex organics during the early stages of star and planet formation. The explicit treatment of photoproduct absorption during irradiation also illustrates the coupled physical-chemical evolution that must be considered in any realistic ice-processing model.

major comments (2)

[Radiative-transfer model] Radiative-transfer model (described in the methods/results): the correction for effective absorbed fluence assumes UV absorption cross sections for the photoproducts that are not independently measured or validated against pure-ethanol benchmarks. Because the derived photodestruction cross sections are obtained only after this correction, any systematic error in the assumed opacities or optical-depth evolution directly propagates into the reported composition dependence and the headline value of ~1.6 × 10^{-17} cm²/photon.
[Results on cross sections] Results section on cross-section extraction: the manuscript presents the final corrected cross sections but does not show the raw fluence-corrected decay curves, the sensitivity of the derived values to the photoproduct opacity assumptions, or error bars that incorporate model uncertainty. Without these, it is not possible to judge whether the apparent stabilization trend is statistically significant or an artifact of the correction procedure.

minor comments (2)

[Abstract] The abstract states that photoproducts play a significant role in later-stage absorption but does not quantify the fractional contribution or show the corresponding time-dependent optical-depth curves; adding a brief summary or reference to a supplementary figure would improve clarity.
[Figures] Figure captions should explicitly label each trace with the initial ethanol:CO ratio and indicate whether the plotted quantity is raw absorbance or fluence-corrected column density.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and detailed report. The comments highlight important aspects of the radiative-transfer model and the presentation of results that warrant clarification and expansion. We address each point below and will revise the manuscript accordingly to improve transparency and allow better evaluation of the robustness of the derived photodestruction cross sections.

read point-by-point responses

Referee: [Radiative-transfer model] Radiative-transfer model (described in the methods/results): the correction for effective absorbed fluence assumes UV absorption cross sections for the photoproducts that are not independently measured or validated against pure-ethanol benchmarks. Because the derived photodestruction cross sections are obtained only after this correction, any systematic error in the assumed opacities or optical-depth evolution directly propagates into the reported composition dependence and the headline value of ~1.6 × 10^{-17} cm²/photon.

Authors: We agree that the photoproduct UV absorption cross sections used in the model are estimated rather than directly measured in dedicated experiments. These estimates draw from literature values for related species and are constrained by consistency checks against our pure-ethanol (1:0) irradiation data. While independent validation for every photoproduct was outside the scope of this proof-of-principle study, the model correctly reproduces the observed saturation behavior in the pure-ethanol case. In the revised manuscript we will add an explicit subsection detailing the sources of the assumed opacities, the rationale for each choice, and a quantitative sensitivity analysis showing the effect of ±30% variations in photoproduct cross sections on the final ethanol photodestruction values. This will be accompanied by a brief discussion of remaining model limitations. revision: yes
Referee: [Results on cross sections] Results section on cross-section extraction: the manuscript presents the final corrected cross sections but does not show the raw fluence-corrected decay curves, the sensitivity of the derived values to the photoproduct opacity assumptions, or error bars that incorporate model uncertainty. Without these, it is not possible to judge whether the apparent stabilization trend is statistically significant or an artifact of the correction procedure.

Authors: We accept that the current presentation omits intermediate results needed for independent assessment. The revised manuscript will include new figures (or an expanded results section) showing the fluence-corrected ethanol decay curves for all mixtures, a sensitivity plot illustrating how the extracted cross sections respond to changes in the assumed photoproduct opacities, and updated error bars that propagate the dominant model uncertainties (optical-depth evolution and opacity assumptions). These additions will enable readers to evaluate the statistical significance of the CO-induced stabilization trend directly. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation grounded in experimental data with independent physical correction

full rationale

The paper measures ethanol IR band decay rates under UV irradiation for varying CO mixtures, develops a radiative-transfer model based on composition-dependent absorption to compute effective fluence, and computes photodestruction cross sections from the ratio of observed decay to corrected fluence. This chain does not reduce to self-definition or fitted inputs by construction; the model applies standard radiative transfer principles to evolving optical depth, and the final composition dependence emerges from the experimental trends after correction rather than being imposed by the model itself. No self-citation load-bearing or ansatz smuggling is evident in the provided derivation steps. The result remains falsifiable against independent fluence measurements or pure-ethanol benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The claim depends on experimental observations interpreted through a custom radiative transfer model whose internal parameters and assumptions are not detailed in the provided abstract.

free parameters (1)

effective UV fluence correction factors
Derived from the radiative transfer model to adjust observed destruction for actual absorbed photons by ethanol.

axioms (1)

domain assumption Photoproducts significantly absorb incident UV photons in later irradiation stages, requiring model correction for accurate cross sections.
Invoked to explain the need for the radiative-transfer model in deriving composition-dependent photostability.

pith-pipeline@v0.9.0 · 5899 in / 1399 out tokens · 43111 ms · 2026-05-18T03:21:17.782038+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

A radiative-transfer model has been developed to more accurately account for the influence of the composition of the ice on the effective photon flux experienced by the molecules embedded within the ice. ... By evaluating photodestruction cross sections as a function of the initial ice composition, we found that CO exerts a stabilizing effect on ethanol.
IndisputableMonolith/Foundation/AbsoluteFloorClosure.lean absolute_floor_iff_bare_distinguishability unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

The model reveals that, during later stages of irradiation, photoproducts play a significant role in the absorbing of incident photons

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