[astro-ph.GA] We use kinetic Monte Carlo (KMC) simulations to study molecular hydrogen formation on carbonaceous dust grain surfaces, validated against recent laboratory measurements of H2 formation on coronene films at temperatures from 10 to 250 K.
The model uses a three-dimensional amorphous carbon lattice with heterogeneous physisorption (45±5 meV) and chemisorption (1.75±0.25 eV) sites, and tracks both Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) formation channels within a stochastic Gillespie event-driven framework.
The model reproduces the measured efficiency curve within the experimental uncertainties, including the isothermal (constant surface temperature) measurements at 100 – 250 K. The simulations correctly describe the phase boundary between the LH and ER driven processes as functions of grain temperature and the observed crossover.
Under interstellar medium conditions, 10 – 250 K and n = 10 – 104 cm3, the model predicts three distinct regimes for the formation efficiency ϵ, the fraction of impinging H atoms released as H2. At 10 K diffusion is slow and ϵ≈0.06. Between 20 K and 80 K, LH dominates and ϵ≈0.28. Above 150 K, an ER plateau at ϵ=0.19 is sustained by chemisorption-trapped H atoms.
The LH-to-ER crossover occurs between 100 and 120 K. At 100 K we observe a 16% density-dependent stochastic enhancement, which rate-equation models cannot capture. At Tdust = 60 K, n = 103 cm3 we find the ratio of H2 formation to free-fall time tH2/tff≈0.93, so dust-catalysed H2 chemistry can keep pace with gravitational collapse in high-redshift star-forming environments.
Aryav Das, Julia Gao, Daniel Vrinceanu, H. R. Sadeghpour
Comments: 21 pages, 18 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2608.16149 [astro-ph.GA] (or arXiv:2608.16149v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2608.16149
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Submission history
From: Daniel Vrinceanu
[v1] Mon, 17 Aug 2026 06:01:56 UTC (1,799 KB)
https://arxiv.org/abs/2608.16149
astrobiology, astrochemistry, interstellar,
