Contributions From Grain Surface and Gas Phase Chemistry to the Formation of Methyl Formate and Its Structural Isomers

Laas, J.; Garrod, R. T.; Herbst, Eric; Weaver, Susanna L. Widicus

doi:10.1088/0004-637x/728/1/71

Cited by 117 publications

(165 citation statements)

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“…Our grain-surface network is also from Laas et al (2011) which itself is derived from Garrod & Herbst (2006) and Garrod et al (2008) with the grain-surface reaction rates calculated according to Hasegawa et al (1992). We assume a density of surface sites equal to ≈1.5 × 10 15 cm −2 and for the barrier between surface sites, E b ≈ 0.3E D , where E D is the binding (desorption) energy to the grain surface of the reactant of interest.…”

Section: Chemical Modelmentioning

confidence: 99%

Complex organic molecules in protoplanetary disks

Walsh

Millar

Nomura

et al. 2014

A&A

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223

356

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Context. Protoplanetary disks are vital objects in star and planet formation, possessing all the material, gas and dust, which may form a planetary system orbiting the new star. Small, simple molecules have traditionally been detected in protoplanetary disks; however, in the ALMA era, we expect the molecular inventory of protoplanetary disks to significantly increase. Aims. We investigate the synthesis of complex organic molecules (COMs) in protoplanetary disks to put constraints on the achievable chemical complexity and to predict species and transitions which may be observable with ALMA. Methods. We have coupled a 2D steady-state physical model of a protoplanetary disk around a typical T Tauri star with a large gas-grain chemical network including COMs. We compare the resulting column densities with those derived from observations and perform ray-tracing calculations to predict line spectra. We compare the synthesised line intensities with current observations and determine those COMs which may be observable in nearby objects. We also compare the predicted grain-surface abundances with those derived from cometary comae observations. Results. We find COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances ∼10 −6 -10 −4 that of the H nuclei number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances than their grain-surface equivalents, ∼10 −12 -10 −7 . Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. There is reasonable agreement with several line transitions of H 2 CO observed towards T Tauri star-disk systems. There is poor agreement with HC 3 N lines observed towards LkCa 15 and GO Tau and we discuss possible explanations for these discrepancies. The synthesised line intensities for CH 3 OH are consistent with upper limits determined towards all sources. Our models suggest CH 3 OH should be readily observable in nearby protoplanetary disks with ALMA; however, detection of more complex species may prove challenging, even with ALMA "Full Science" capabilities. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets (and other planetesimals) formed via the coagulation of icy grains in the Sun's natal disk.

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Section: Chemical Modelmentioning

confidence: 99%

Complex organic molecules in protoplanetary disks

Walsh

Millar

Nomura

et al. 2014

A&A

Self Cite

223

356

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“…As described in the introduction, the new generation of COMs formation models predicts that COMs are synthesized during the warm-up phase thanks to the increased mobility of radicals, formed on the grain surfaces during the previous cold phase (Garrod & Herbst 2006;Garrod et al 2008;Aikawa et al 2008;Awad et al 2010;Laas et al 2011). The abundance of radicals in the mantles during the cold phase is, therefore, a key point.…”

Section: C) Photolysismentioning

confidence: 99%

“…Finally, even the branching ratios of species caused by the photodissociation in the gas phase are very poorly known (e.g., Laas et al 2011). In this context, various authors omit the photolysis in their model (e.g., Chang et al 2007;Cuppen et al 2009).…”

Section: C) Photolysismentioning

confidence: 99%

“…Our model differs from most previous published models because it treats the multilayer and porous structure of the iced mantles. In the mentioned previous models (Garrod & Herbst 2006;Garrod et al 2008;Aikawa et al 2008;Awad et al 2010;Laas et al 2011), COMs are synthesized during the warmup phase thanks to the increased mobility of radicals, formed on the grain surfaces during the previous cold phase. The abundance of radicals in the mantles during the cold phase is, therefore, a key point.…”

Section: Introductionmentioning

confidence: 99%

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Multilayer modeling of porous grain surface chemistry

Taquet

Ceccarelli

Kahane

2012

A&A

145

157

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Context. Mantles of iced water mixed with carbon monoxyde, formaldehyde, and methanol are formed during the so-called prestellar core phase. In addition, radicals are also thought to be formed on the grain surfaces, and to react to form complex organic molecules later on, during the so-called warm-up phase of the protostellar evolution. Aims. We aim to study the formation of the grain mantles during the prestellar core phase and the abundance of formaldehyde, methanol, and radicals trapped in them. Methods. We have developed a macrosopic statistic multilayer model that follows the formation of grain mantles with time and that includes two effects that may increase the number of radicals trapped in the mantles: i) during the mantle formation, only the surface layer is chemically active and not the entire bulk; and ii) the porous structure of grains allows the trapping reactive particles. The model considers a network of H, O, and CO forming neutral species such as water, CO, formaldehyde, and methanol, plus several radicals. We ran a large grid of models to study the impact of the mantle multilayer nature and grain porous structure. In addition, we explored how the uncertainty of other key parameters influences the mantle composition. Results. Our model predicts relatively high abundances of radicals, especially of HCO and CH 3 O (10 −9 −10 −7 ). In addition, the multilayer approach enables us to follow the chemical differentiation within the grain mantle, showing that the mantles are far from being uniform. For example, methanol is mostly present in the outer layers of the mantles, whereas CO and other reactive species are trapped in the inner layers. The overall mantle composition depends on the density and age of the prestellar core as well as on some microscopic parameters, such as the diffusion energy and the hydrogenation reactions activation energy. Comparison with observations allows us to constrain the value of the last two parameters (0.5-0.65 and 1500 K, respectively) and provide some indications on the physical conditions during the formation of the ices.

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“…The core in Sgr B2, designated the Sgr B2(N) Large Molecule Heimat source or Sgr B2(N-LMH) by Snyder (2006), has the highest column densities of CH 3 CH 2 CN of all sources studied so far (∼9.6 × 10 16 cm −2 ) (Miao et al 1995;Kuan et al 1996;Miao & Snyder 1997). Formation mechanisms Full Table 3 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A2 for CH 3 CH 2 CN and other COMs were discussed by Laas et al (2011), Garrod et al (2008), Belloche et al (2009Belloche et al ( , 2014.…”

Section: Introductionmentioning

confidence: 99%

The millimeter and sub-millimeter rotational spectrum of triple ¹³C-substituted ethyl cyanide

Pienkina

Margulès

Motiyenko

et al. 2017

A&A

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Context.A recently published astronomical detection of all three doubly 13 C-substituted ethyl cyanides toward Sgr B2(N2) motivated us to investigate triple 13 C isotopic species that are expected to be also present in the ISM. Aims. We aim to present an experimental study of the rotational spectrum of triple 13 C-substituted ethyl cyanide, 13 CH 13 3 CH 13 2 CN, in the frequency range 150-990 GHz. We want to use the determined spectroscopic parameters for searching for 13 CH 13 3 CH 13 2 CN in ALMA data. The main objective of this work is to provide accurate frequency predictions to search for this molecule in the Galactic center source Sagittarius B2(N) and to facilitate its detection in space.Methods. The laboratory rotational spectrum of 13 CH 13 3 CH 13 2 CN has been recorded with the Lille's fast DDS solid-state spectrometer between 150 GHz and 990 GHz. Results. More than 4000 rotational transitions were identified in the laboratory. The quantum numbers reach J = 115 and K a = 39. Watson's Hamiltonian in the A and S reductions were used to analyze the spectra. Accurate spectroscopic parameters were determined. The rotational spectra of the 13 C containing species CH 3 CH 2 CN have been assigned, thus allowing the determination of the rotational and centrifugal distortion constants

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Contributions From Grain Surface and Gas Phase Chemistry to the Formation of Methyl Formate and Its Structural Isomers

Cited by 117 publications

References 19 publications

Complex organic molecules in protoplanetary disks

Complex organic molecules in protoplanetary disks

Multilayer modeling of porous grain surface chemistry

The millimeter and sub-millimeter rotational spectrum of triple ¹³C-substituted ethyl cyanide

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Contributions From Grain Surface and Gas Phase Chemistry to the Formation of Methyl Formate and Its Structural Isomers

Cited by 117 publications

References 19 publications

Complex organic molecules in protoplanetary disks

Complex organic molecules in protoplanetary disks

Multilayer modeling of porous grain surface chemistry

The millimeter and sub-millimeter rotational spectrum of triple 13C-substituted ethyl cyanide

Contact Info

Product

Resources

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The millimeter and sub-millimeter rotational spectrum of triple ¹³C-substituted ethyl cyanide