Ligterink, NFW, Walsh, C orcid.org/0000-0001-6078-786X, Bhuin, RG et al. (3 more authors) (2018) Methanol ice co-desorption as a mechanism to explain cold methanol in the gas-phase. Astronomy and Astrophysics, 612. A88. ISSN 0004-6361
Abstract
Context. Methanol is formed via surface reactions on icy dust grains. Methanol is also detected in the gas-phase at temperatures below its thermal desorption temperature and at levels higher than can be explained by pure gas-phase chemistry. The process that controls the transition from solid state to gas-phase methanol in cold environments is not understood.
Aims. The goal of this work is to investigate whether thermal CO desorption provides an indirect pathway for methanol to co-desorb at low temperatures.
Methods. Mixed CH₃OH:CO/CH₄ ices were heated under ultra-high vacuum conditions and ice contents are traced using RAIRS (reflection absorption IR spectroscopy), while desorbing species were detected mass spectrometrically. An updated gas-grain chemical network was used to test the impact of the results of these experiments. The physical model used is applicable for TW Hya, a protoplanetary disk in which cold gas-phase methanol has recently been detected.
Results. Methanol release together with thermal CO desorption is found to be an ineffective process in the experiments, resulting in an upper limit of ≤ 7.3 × 10−7 CH₃OH molecules per CO molecule over all ice mixtures considered. Chemical modelling based on the upper limits shows that co-desorption rates as low as 10−6 CH₃OH molecules per CO molecule are high enough to release substantial amounts of methanol to the gas-phase at and around the location of the CO thermal desorption front in a protoplanetary disk. The impact of thermal co-desorption of CH₃OH with CO as a grain-gas bridge mechanism is compared with that of UV induced photodesorption and chemisorption.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | (c) 2018, ESO. Reproduced with permission from Astronomy & Astrophysics. |
Keywords: | astrochemistry; methods: laboratory: molecular; techniques: spectroscopic; molecular processes; ultraviolet: ISM |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds) > Astrophysics (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 14 May 2018 16:16 |
Last Modified: | 14 May 2018 16:16 |
Status: | Published |
Publisher: | EDP Sciences |
Identification Number: | 10.1051/0004-6361/201731893 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:130761 |