Water ice deposition and growth in molecular clouds

Rawlings, J. M. C.; Williams, D. A.

doi:10.1093/mnras/staa3578

Cited by 5 publications

(1 citation statement)

References 49 publications

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“…The model is based on a simple one-point, dynamically static, application of the STARCHEM model that we have used in other studies (e.g. Rawlings & Williams 2021 ). For the purpose of our study, we assume that the system is well-evolved and in chemical quasi-equilibrium, which is consistent with our understanding of the conditions within dense cores and pre-stellar star-forming regions (e.g.…”

Section: T H E M O D E L O F S P O R a D I C D E S O R P T I O Nmentioning

confidence: 89%

Towards a better understanding of ice mantle desorption by cosmic rays

Rawlings

2022

Monthly Notices of the Royal Astronomical Society

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The standard model of cosmic ray heating-induced desorption of interstellar ices is based on a continuous representation of the sporadic desorption of ice mantle components from classical ($0.1\, \mu$m) dust grains. This has been re-evaluated and developed to include tracking the desorption through (extended) grain cooling profiles, consideration of grain size-dependencies and constraints to the efficiencies. A model was then constructed to study the true, sporadic, nature of the process with possible allowances from species co-desorption and whole mantle desorption from very small grains. The key results from the study are that the desorption rates are highly uncertain, but almost certainly significantly larger than have been previously determined. For typical interstellar grain size distributions it is found that the desorption is dominated by the contributions from the smallest grains. The sporadic desorption model shows that, if the interval between cosmic ray impacts is comparable to, or less than, the freeze-out timescale, the continuous representation is inapplicable; chemical changes may occur on very long timescales, resulting in strong gas phase chemical enrichments that have very non-linear dependences on the cosmic ray flux. The inclusion of even limited levels of species co-desorption and/or the contribution from very small grains further enhances the rates, especially for species such as H2O. In general we find that cosmic ray heating is the dominant desorption mechanism in dark environments. These results may have important chemical implications for protostellar and protoplanetary environments.

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Section: T H E M O D E L O F S P O R a D I C D E S O R P T I O Nmentioning

confidence: 89%

Towards a better understanding of ice mantle desorption by cosmic rays

Rawlings

2022

Monthly Notices of the Royal Astronomical Society

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Interstellar Ices and Solid-state Chemistry as a Route to Molecular Complexity

2023

Astrochemistry

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Dust grains in shielded regions of quiescent interstellar clouds are observed to accumulate mantles of simple ices containing molecules of H2O, CO, and CO2, with minor amounts of CH3OH, NH3, and a few other species. Some of these simple ice molecules (e.g., CO) may simply adhere to the surface from the gas. H-additions to surface species such as atomic oxygen may generate abundant ice molecules such as H2O. Other reactions in these simple ices may generate species such as CH3OH and CO2. All of these simple ice species are important in interstellar chemistry because they can be the molecular feedstock from which more complex species may form in solid-state chemistry that occurs when the ice is suitably energized by UV, X-ray, or energetic particle irradiations. Products of greater complexity promoted by these energy inputs may include acetaldehyde (CH3CHO), dimethyl ether (CH3OCH3), ethanol (CH3CH2OH), and ethylene glycol (CH2OH)2. We discuss some experimental evidence for such chemical processing. Some of these more complex species arising in these experiments may even be of astrobiological interest, such as glycine (NH2CH2COOH) and formamide (HCONH2).

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A multi-grain multi-layer astrochemical model with variable desorption energy for surface species

Kalvāns,

Kalniņa,

Veitners

2024

A&A

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Interstellar surface chemistry is a complex process that occurs in icy layers that have accumulated onto grains of different sizes. The efficiency of the surface processes often depends on the immediate environment of the adsorbed molecules. We investigated how gas-grain chemistry changes when the surface molecule binding energy is modified, depending on the properties of the surface. In a gas-grain astrochemical model, molecular binding energy gradually changes for three different environments -- (1) the bare grain surface, (2) polar water-dominated ices, and (3) weakly polar carbon monoxide-dominated ices. In addition to diffusion, evaporation, and chemical desorption, photodesorption was also made binding energy-dependent, in line with experimental results. These phenomena occur in a collapsing prestellar core model that considers five grain sizes with ices arranged into four layers. Variable desorption energy moderately affects gas-grain chemistry. Bare-grain effects slow down ice accumulation, while easier diffusion of molecules on weakly polar ices promotes the production of carbon dioxide. Efficient chemical desorption from bare grains significantly delays the appearance of the first ice monolayer. The combination of multiple aspects of grain surface chemistry creates a gas-ice balance that is different from simpler models. The composition of the interstellar ices is regulated by several binding-energy dependent desorption mechanisms. Their actions overlap in time and space, explaining the similar proportions of major ice components (water and carbon oxides) observed in all directions.

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Water ice deposition and growth in molecular clouds

Cited by 5 publications

References 49 publications

Towards a better understanding of ice mantle desorption by cosmic rays

Towards a better understanding of ice mantle desorption by cosmic rays

Interstellar Ices and Solid-state Chemistry as a Route to Molecular Complexity

A multi-grain multi-layer astrochemical model with variable desorption energy for surface species

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