Methoxymethanol formation starting from CO hydrogenation
Astronomy and Astrophysics, vol. 659, pp. A65
Abstract
Context. Methoxymethanol (CH3OCH2OH) has been identified through gas-phase signatures in both high- and low-mass star-forming regions. Like several other C-, O-, and H-containing complex organic molecules (COMs), this molecule is expected to form upon hydrogen addition and abstraction reactions in CO-rich ice through radical recombination of CO hydrogenation products. Aims. The goal of this work is to experimentally and theoretically investigate the most likely solid-state methoxymethanol reaction channel – the recombination of CH2OH and CH3O radicals – for dark interstellar cloud conditions and to compare the formation efficiency with that of other species that were shown to form along the CO-hydrogenation line. We also investigate an alternative hydrogenation channel starting from methyl formate. Methods. Hydrogen atoms and CO or H2CO molecules were co-deposited on top of predeposited H2O ice to mimic the conditions associated with the beginning of “rapid” CO freeze-out. The formation of simple species was monitored in situ using infrared spectroscopy. Quadrupole mass spectrometry was used to analyze the gas-phase COM composition following a temperature-programmed desorption. Monte Carlo simulations were used for an astrochemical model comparing the methoxymethanol formation efficiency with that of other COMs. Results. The laboratory identification of methoxymethanol is found to be challenging, in part because of diagnostic limitations, but possibly also because of low formation efficiencies. Nevertheless, unambiguous detection of newly formed methoxymethanol has been possible in both CO+H and H2CO+H experiments. The resulting abundance of methoxymethanol with respect to CH3OH is about 0.05, which is about six times lower than the value observed toward NGC 6334I and about three times lower than the value reported for IRAS 16293B. Astrochemical simulations predict a similar value for the methoxymethanol abundance with respect to CH3OH, with values ranging between 0.03 and 0.06. Conclusions. We find that methoxymethanol is formed by co-deposition of CO and H2CO with H atoms through the recombination of CH2OH and CH3O radicals. In both the experimental and modeling studies, it is found that the efficiency of this channel alone is not sufficient to explain the observed abundance of methoxymethanol with respect to methanol. The rate of a proposed alternative channel, the direct hydrogenation of methyl formate, is found to be even less efficient. These results suggest that our knowledge of the reaction network is incomplete or involving alternative solid-state or gas-phase formation mechanisms.
Authors 10
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Leiden University · Max Planck Institute for Astronomy · Leiden Observatory
Affiliation as printed
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
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Affiliation as printed
Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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Leiden University · Ural Federal University · Leiden Observatory
Affiliation as printed
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
Research Laboratory for Astrochemistry, Ural Federal University, Kuibysheva St. 48, 620026 Ekaterinburg, Russia
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Leiden University · Max Planck Institute for Astronomy · Leiden Observatory · Friedrich Schiller University Jena
Affiliation as printed
Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, 07743 Jena, Germany
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Leiden University · Goddard Space Flight Center · Leiden Observatory
Affiliation as printed
Current address: Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Thanja Lamberts Aachen Laboratory for Astrophysics, Leiden Observatory Leiden Institute of Chemistry, Gorlaeus Laboratories
Leiden University · Leiden Observatory
Affiliation as printed
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands
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Queen Mary University of London
Affiliation as printed
School of Electronic Engineering and Computer Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK
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National Radio Astronomy Observatory · Center for Astrophysics Harvard & Smithsonian · Massachusetts Institute of Technology
Affiliation as printed
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
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Affiliation as printed
Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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Leiden University · Leiden Observatory
Affiliation as printed
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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