Are gas-phase models of interstellar chemistry tenable? The case of methanol

Garrod, R. T.; Park, In Hee; Caselli, P.; Herbst, Eric

doi:10.1039/b516202e

Cited by 156 publications

(148 citation statements)

References 31 publications

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“…Methanol has been observed in interstellar ices and has been proposed as a good starting point for the formation of more complex species (Ö berg et al 2009). The hypothesis that interstellar methanol forms in the solid phase has been recently supported by experimental and modeling work, showing that the gas-phase route via ion-neutral reactions is less efficient than previously assumed (Geppert et al 2005;Garrod et al 2006). However, the first studies on solid CO hydrogenation by two different groups yielded conflicting results: in one study (Hiraoka et al 2002) only the formation of H 2 CO was reported, whereas in the other study also CH 3 OH was observed (Watanabe and Kouchi 2002).…”

Section: Surface Formation Of Methanolmentioning

confidence: 81%

Surface formation routes of interstellar molecules: hydrogenation reactions in simple ices

Ioppolo

Cuppen

Linnartz

2011

Rend. Fis. Acc. Lincei

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It has been a long standing problem in astrochemistry to explain how molecules can form in a highly dilute environment such as the interstellar medium. In recent years it has become clear that not only ion/radical-molecule gas-phase reactions, but also solid state reactions on icy dust grains play an important role in the formation of new species. In order to investigate the underlying processes, laboratory based experiments are needed to simulate surface reactions induced by photon (UV) processing or particle (atom, cosmic ray, electron) bombardment of interstellar ice analogs. Here, the latest research performed on SURFace REaction SImulation DEvice (SURFRESIDE), one of the ultra-high vacuum setups in the Sackler Laboratory for Astrophysics in Leiden is reviewed. The focus is on hydrogenation, i.e., H-atom addition reactions in interstellar ice analogs for astronomically relevant temperatures. We discuss how molecules form when CO and O 2 containing ices are exposed to thermal hydrogen atoms under fully controlled experimental conditions. Surface formation schemes for interstellar relevant species, such as solid methanol, water, and carbon dioxide are investigated and chemical links between molecular species in space are discussed.

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Section: Surface Formation Of Methanolmentioning

confidence: 81%

Surface formation routes of interstellar molecules: hydrogenation reactions in simple ices

Ioppolo

Cuppen

Linnartz

2011

Rend. Fis. Acc. Lincei

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“…Methanol is expected to form via successive hydrogenation of CO on the surface of dust grains and then partially released in the gas phase upon formation (i.e., part of the formation energy is used to evaporate, in a process called reactive desorption; Garrod et al 2006) and/or upon photo-desorption by UV photons produced by cosmic-ray impacts with H 2 molecules (Prasad & Tarafdar 1983). Evaporated methanol will then freeze-out onto dust grains in a time scale inversely proportional to the gas number density (∼10 9 /n H yr; van Dishoeck et al 1993).…”

Section: Discussionmentioning

confidence: 99%

Deuterated methanol in the pre-stellar core L1544

Bizzocchi

Caselli

Spezzano

et al. 2014

A&A

104

152

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Context. High methanol (CH 3 OH) deuteration has been revealed in Class 0 protostars with the detection of singly, doubly, and even triply D-substituted forms. Methanol is believed to form during the pre-collapse phase via gas-grain chemistry and then eventually injected into the gas when the heating produced by the newly formed protostar sublimates the grain mantles. The molecular deuterium fraction of the warm gas is thus a relic of the cold pre-stellar era and provides hints of the past history of the protostars. Aims. Pre-stellar cores represent the preceding stages in the process of star formation. We aim at measuring methanol deuteration in L1544, a prototypical dense and cold core on the verge of gravitational collapse. The aim is to probe the deuterium fractionation process while the "frozen" molecular reservoir is accumulated onto dust grains. Methods. Using the IRAM 30 m telescope, we mapped the methanol emission in the pre-stellar core L1544 and observed singly deuterated methanol (CH 2 DOH and CH 3 OD) towards the dust peak of L1544. Non-LTE radiative transfer modelling was performed on three CH 3 OH emissions lines at 96.7 GHz, using a Bonnor-Ebert sphere as a model for the source. We have also assumed a centrally decreasing abundance profile to take the molecule freeze-out in the inner core into account. The column density of CH 2 DOH was derived assuming LTE excitation and optically thin emission. Results. The CH 3 OH emission has a highly asymmetric morphology, resembling a non-uniform ring surrounding the dust peak, where CO is mainly frozen onto dust grains. The observations provide an accurate measure of methanol deuteration in the cold pre-stellar gas. The derived abundance ratio is [CH 2 DOH]/[CH 3 OH] = 0.10 ± 0.03, which is significantly smaller than the ones found in lowmass Class 0 protostars and smaller than the deuterium fraction measured in other molecules towards L1544. The singly-deuterated form CH 3 OD was not detected at 3σ sensitivity of 7 mK km s −1 , yielding a lower limit of [CH 2 DOH]/[CH 3 OD] ≥ 10, consistent with previous measurements towards Class 0 protostars. Conclusions. The low deuterium fractionation observed in L1544 and the morphology of the CH 3 OH emission suggest that we are mainly tracing the outer parts of the core, where CO just started to freeze-out onto dust grains.

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“…Garrod et al (2006) conclude that the production of methanol is carried out on the surfaces of dust grains followed by desorption into the gas. The X CH 3 OH values in G11.P11 could then be produced by desorption of icy mantles on the dust grains.…”

Section: Ch 3 Oh Abundancesmentioning

confidence: 99%

High-angular resolution observations of methanol in the infrared dark cloud core G11.11-0.12P1

Gómez

Wyrowski

Pillai

et al. 2011

A&A

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Recent studies suggest that infrared dark clouds (IRDCs) have the potential of harboring the earliest stages of massive star formation and indeed evidence for this is found toward distinct regions within them. We present a study with the Plateau de Bure Interferometer of a core in the archetypal filamentary IRDC G11.11-0.12 of a few arcsecond resolution to determine its physical and chemical structures. The data consist of continuum and line observations covering the C 34 S 2 → 1 line and the methanol 2 k → 1 k v t = 0 lines at 3 mm and the methanol 5 k → 4 k v t = 0 lines at 1 mm. Our observations show extended emission in the continuum at 1 and 3 mm. The methanol 2 k → 1 k v t = 0 emission has three maxima extending over a 1 pc scale (when merged with single-dish short-spacing observations); one of the maxima is spatially coincident with the continuum emission. The fitting results show an enhanced methanol fractional abundance (∼3 × 10 −8 ) at the central peak with respect to the other two peaks, where it decreases by about an order of magnitude (∼4−6 × 10 −9 ). Evidence of extended 4.5 μm emission, "wings" in the CH 3 OH 2 k → 1 k spectra, and CH 3 OH abundance enhancements point to the presence of an outflow in the east-west direction. In addition, we find a gradient of ∼4 km s −1 in the same direction, which we interpret as being produced by an outflow(s)-cloud interaction.

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Are gas-phase models of interstellar chemistry tenable? The case of methanol

Cited by 156 publications

References 31 publications

Surface formation routes of interstellar molecules: hydrogenation reactions in simple ices

Surface formation routes of interstellar molecules: hydrogenation reactions in simple ices

Deuterated methanol in the pre-stellar core L1544

High-angular resolution observations of methanol in the infrared dark cloud core G11.11-0.12P1

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