Simulation Of Proton Radiolysis Of H2O And O2 Ices With The Nautilus Code

The radiolysis effect of cosmic rays (CRs) plays an important role in the chemistry in molecular clouds. CRs can dissociate the molecules on dust grains, producing reactive suprathermal species and radicals which facilitate the formation of large molecules. We add the radiolysis process and some relevant reactions into the Nautilus astrochemical code.

By adjusting some parameters, we investigate the sensitivity of the simulation results of the H₂O ice on the removal of reaction-diffusion competition, the removal of non-diffusive chemistry, and the desorption energies of the suprathermal species.

We find the model, with a few adjustments of the chemistry, can reproduce the steady-state [H₂O₂]/[H₂O] and [O₃]/[O₂]_0 abundance ratios in the H₂O and O₂ radiolysis experiments at any CR flux in the experiments. These adjustments in the model do not fully reproduce the fluence required to reach the steady state. It tends also to overestimate the destruction of H₂O as measured in H₂O radiolysis experiments.

We show that reducing the G-values of H₂O radiolysis, which implies an increase in the efficiency of immediate reformation of water locally after ion impact, leads to simulated H₂O destruction rates closer to the experiments. The effect of reaction-diffusion competition on the simulation results of H₂2O ice is significant at ζ≲10⁻¹⁴ s⁻¹.

The non-diffusive chemistry affects the simulation results at 16 K but not 77K, while the results are sensitive to the desorption energies of suprathermal H, O, O₃ and OH at 77 K. Our results show that the steady-state [H₂O₂]/[H₂O] and [O₃]/[O₂]_0 in experiments can be reproduced by fine-tuning the chemical model, but still call for more constraints on the intermediate pathways in the radiolysis processes, especially the ion chemistry in the ice bulk, as well as activation barriers and branching ratios of the reactions in the network.

Tian-Yu Tu, Valentine Wakelam, Jean-Christophe Loison, Marin Chabot, Emmanuel Dartois, Yang Chen

Comments: 12 pages, 8 figures, accepted for publication in A&A, abstract adjusted for the requirements of ArXiv
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2602.19996 [astro-ph.GA] (or arXiv:2602.19996v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2602.19996
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Submission history
From: Tianyu Tu
[v1] Mon, 23 Feb 2026 16:03:16 UTC (123 KB)
https://arxiv.org/abs/2602.19996
Astrobiology,