Microscopic simulation of methanol and formaldehyde ice formation in cold dense cores

By H. Cuppen, E. Dishoeck, E. Herbst, A. Tielens. 2009

141 citations recorded by the source corpus.

Context. Methanol and its precursor formaldehyde are among the most studied organic molecules in the interstellar medium and are abundant in the gaseous and solid phases. We recently developed a model to simulate CO hydrogenation via H atoms on interstellar ice surfaces, the most important interstellar route to H 2 CO and CH 3 OH, under laboratory conditions. Aims. We extend this model to simulate the formation of both organic species under interstellar conditions, including freeze-out from the gas and hydrogenation on surfaces. Our aim is to compare calculated abundance ratios with observed values and with the results of prior models. Methods. Our model utilises the continuous-time, random-walk Monte Carlo method, which - unlike other approaches - is able to simulate microscopic grain-surface chemistry over the long timescales in interstellar space, including the layering of ices during freeze-out. Results. Simulations under different conditions, including density and temperature, have been performed. We find that H 2 CO and CH 3 OH form efficiently in cold dense cores or the cold outer envelopes of young stellar objects. The grain mantle is found to have a layered structure with CH 3 0H on top. The species CO and H 2 CO are found to exist predominantly in the lower layers of ice mantles where they are not available for hydrogenation at late times. This finding is in contrast with previous gas-grain models, which do not take into account the layering of the ice. Some of our results can be reproduced by a simple quasi-steady-state analytical model that focuses on the outer layer. Conclusions. Observational solid H 2 CO/CH 3 OH and CO/CH 3 OH abundance ratios in the outer envelopes of an assortment of young stellar objects agree reasonably well with our model results, which also suggest that the large range in CH 3 OH/H 2 O observed abundance ratios is due to variations in the evolutionary stages. Finally, we conclude that the limited chemical network used here for surface reactions apparently does not alter the overall conclusions.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Biomedical Engineering

View Paper: https://www.semanticscholar.org/paper/6f80db1ebf21ec8f4d96aa67849ed27e0dcec664

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. R. Garrod
2. E. Herbst
3. V. Wakelam
4. K. Oberg
5. E. V. van Dishoeck
6. E. Dishoeck
7. H. Cuppen
8. H. Linnartz

In Atomic and Molecular Physics, and Optics

1. R. Garrod
2. V. Wakelam
3. E. Herbst
4. E. V. van Dishoeck
5. T. Pauly
6. K. Oberg
7. S. Ioppolo
8. H. Linnartz

In Biomedical Engineering

1. R. Garrod
2. V. Wakelam
3. E. Herbst
4. T. Pauly
5. K. Oberg
6. H. Cuppen
7. A. Vasyunin
8. M. Ruaud

Citations in the corpus

• H-atom addition and abstraction reactions in mixed CO, H2CO and CH3OH ices – an extended view on complex organic molecule formation (2016, background): “…(2016) by guest on N ovem ber 20, 2015 http://m nras.oxfordjournals.org/ D ow nloaded from COMs and CO/H2CO/CH3OH ice hydrogenation 1711 abundance of interstellar methanol (Watanabe et al. 2006; Cuppen et al. 2009), but also its deuterium enrichment (Nagaoka et al. 2005; Hidaka et al. 2009).”
• Our astrochemical heritage (2012, unknown): “[7]; [170]; [210]; [120]; [86]; [411]; [410]).”
• Grain Surface Models and Data for Astrochemistry (2017, methodology): “Cuppen et al. (2009) extended the Fuchs et al. (2009) model to simulate in detail the formation of both H2CO and CH3OH under interstellar conditions.”
• ON THE FORMATION OF CO2 AND OTHER INTERSTELLAR ICES (2011, methodology): “Cuppen et al. (2009) estimate that the binding energy to an H2 surface is around 10 times weaker than that for CO.”
• Experimental evidence for glycolaldehyde and ethylene glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions (2015, methodology): “The upper panels show the H−atom low-density case that was not discussed in Cuppen et al. (2009).”
• Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges (2010, background): “Using these barriers, the methanol production can be simulated for interstellar conditions (Cuppen et al. 2009).”
• Observations of the Icy Universe (2015, background): “This then leads to H2CO and CH3OH on a short time scale of ∼ few× 10 4 years, as demonstrated in Monte Carlo simulations (Cuppen et al., 2009), and likely to a host of other CO-derived species, including HNCO (Fedoseev et al., 2015) and CO2 (in the apolar component).”
• THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS (2011, background): “The CO to CH3OH conversion efficiency thus vary in different lines of sight, probably dependent on the H/CO ratio, which may vary with density and collapse time (Cuppen et al. 2009) and cosmic ray flux (Boogert et al. 2011).”
• A COLD COMPLEX CHEMISTRY TOWARD THE LOW-MASS PROTOSTAR B1-b: EVIDENCE FOR COMPLEX MOLECULE PRODUCTION IN ICES (2010, background): “CO:CH3OH ice mixtures are probably common since CH3OH forms from hydrogenation of CO (e.g. Watanabe et al. 2003; Cuppen et al. 2009).”