Complex organic molecules along the accretion flow in isolated and externally irradiated protoplanetary disks

The birth environment of the Sun will have influenced the physical and chemical structure of the pre-solar nebula, including the attainable chemical complexity reached in the disk, important for prebiotic chemistry. The formation and distribution of complex organic molecules (COMs) in a disk around a T Tauri star is investigated for two scenarios: (i) an isolated disk, and (ii) a disk irradiated externally by a nearby massive star. The chemistry is calculated along the accretion flow from the outer disk inwards using a comprehensive network which includes gas-phase reactions, gas-grain interactions, and thermal grain-surface chemistry. Two simulations are performed, one beginning with complex ices and one with simple ices only. For the isolated disk, COMs are transported without major chemical alteration into the inner disk where they thermally desorb into the gas reaching an abundance representative of the initial assumed ice abundance. For simple ices, COMs can efficiently form on grain surfaces under the conditions in the outer disk. Gas-phase COMs are released into the molecular layer via photodesorption. For the irradiated disk, complex ices are also transported inwards; however, they undergo thermal processing caused by the warmer conditions in the irradiated disk which tends to reduce their abundance along the accretion flow. For simple ices, grain-surface chemistry cannot efficiently synthesise COMs in the outer disk because the necessary grain-surface radicals, which tend to be particularly volatile, are not sufficiently abundant on the grain surfaces. Gas-phase COMs are formed in the inner region of the irradiated disk via gas-phase chemistry induced by the desorption of strongly bound molecules such as methanol; hence, the abundances are not representative of the initial molecular abundances injected into the outer disk. These results suggest that the composition of comets formed in isolated disks may differ from those formed in externally irradiated disks with the latter composed of more simple ices.

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Chemical modelling of N-bearing COMs in star-forming regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317006937 ◽

2017 ◽

Vol 13 (S332) ◽

pp. 415-417

Author(s):

David Quénard ◽

Izaskun Jiménez-Serra ◽

Serena Viti ◽

Jonathan Holdship

Keyword(s):

Surface Chemistry ◽

Gas Phase ◽

Organic Molecules ◽

Methyl Isocyanate ◽

Star Forming ◽

Star Forming Regions ◽

Chemical Modelling ◽

Grain Surface ◽

Complex Organic

AbstractThe study of complex organic molecules, and more specifically those of prebiotic interest, is important to understand the chemical richness of star-forming regions. The chemistry of nitrogen bearing molecules such as formamide or methyl isocyanate is poorly constrained. We study different chemical pathways to form and destroy these molecules from both the gas phase and grain surface chemistry. From comparison with observations of four different relevant astrophysical regions, we show that both the gas phase and grain surface chemistry are required to explain the observed abundances of these species.

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Chemical complexity in the Horsehead photodissociation region

Faraday Discussions ◽

10.1039/c3fd00114h ◽

2014 ◽

Vol 168 ◽

pp. 103-127 ◽

Cited By ~ 29

Author(s):

Viviana V. Guzmán ◽

Jérôme Pety ◽

Pierre Gratier ◽

Javier R. Goicoechea ◽

Maryvonne Gerin ◽

...

Keyword(s):

Interstellar Medium ◽

Gas Phase ◽

Thermal Desorption ◽

Organic Molecules ◽

Dense Core ◽

High Spectral Resolution ◽

Complex Molecules ◽

Chemical Complexity ◽

Clean Environment ◽

Complex Organic

The interstellar medium is known to be chemically complex. Organic molecules with up to 11 atoms have been detected in the interstellar medium, and are believed to be formed on the ices around dust grains. The ices can be released into the gas-phase either through thermal desorption, when a newly formed star heats the medium around it and completely evaporates the ices; or through non-thermal desorption mechanisms, such as photodesorption, when a single far-UV photon releases only a few molecules from the ices. The first mechanism dominates in hot cores, hot corinos and strongly UV-illuminated PDRs, while the second dominates in colder regions, such as low UV-field PDRs. This is the case of the Horsehead were dust temperatures are ≃20–30 K, and therefore offers a clean environment to investigate the role of photodesorption. We have carried out an unbiased spectral line survey at 3, 2 and 1mm with the IRAM-30m telescope in the Horsehead nebula, with an unprecedented combination of bandwidth, high spectral resolution and sensitivity. Two positions were observed: the warm PDR and a cold condensation shielded from the UV field (dense core), located just behind the PDR edge. We summarize our recently published results from this survey and present the first detection of the complex organic molecules HCOOH, CH2CO, CH3CHO and CH3CCH in a PDR. These species together with CH3CN present enhanced abundances in the PDR compared to the dense core. This suggests that photodesorption is an efficient mechanism to release complex molecules into the gas-phase in far-UV illuminated regions.

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Interstellar Methanol from the Lab to Protoplanetary Disks

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317005105 ◽

2015 ◽

Vol 11 (A29A) ◽

Author(s):

Maria N. Drozdovskaya ◽

Catherine Walsh ◽

Ruud Visser ◽

Daniel Harsono ◽

Ewine F. van Dishoeck

Keyword(s):

Organic Molecules ◽

Disk Formation ◽

Chemical Complexity ◽

Chemical Models ◽

Collapse Model ◽

Low Mass ◽

Grain Surface ◽

Physical And Chemical ◽

Complex Organic ◽

Insight Into

Interstellar methanol is thought to be the precursor of larger, more complex organic molecules. It holds a central role in many astrochemical models (e.g., Garrod & Herbst 2006). Methanol has also been the focus of several laboratory studies (e.g., Watanabe et al. 2004, Fuchs et al. 2009), in an effort to gain insight into grain-surface chemistry, which potentially builds chemical complexity already in the cold, dark prestellar phase. The case of methanol is a prime example of experimental work having implications on astronomical scales. Drozdovskaya et al. (2014) unified physical and chemical models to simulate infalling material during the birth of a low-mass protostar. An axisymmetric 2D semi-analytic collapse model (Visser et al. 2009), wavelength-dependent radiative transfer calculations with RADMC3D (Dullemond & Dominik 2004) and a comprehensive gas-grain chemical network (Walsh et al. 2014) were used to study two modes of protoplanetary disk formation.

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The GUAPOS project: G31.41+0.31 Unbiased ALMA sPectral Observational Survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038966 ◽

2020 ◽

Vol 644 ◽

pp. A84

Author(s):

C. Mininni ◽

M. T. Beltrán ◽

V. M. Rivilla ◽

A. Sánchez-Monge ◽

F. Fontani ◽

...

Keyword(s):

Acetic Acid ◽

Gas Phase ◽

Organic Molecules ◽

Methyl Formate ◽

Galactic Center ◽

Physical Parameters ◽

Star Forming ◽

Grain Surface ◽

Spectral Survey ◽

Complex Organic

Context. One of the goals of astrochemistry is to understand the degree of chemical complexity that can be reached in star-forming regions, along with the identification of precursors of the building blocks of life in the interstellar medium. To answer such questions, unbiased spectral surveys with large bandwidth and high spectral resolution are needed, in particular, to resolve line blending in chemically rich sources and identify each molecule (especially for complex organic molecules). These kinds of observations have already been successfully carried out, primarily towards the Galactic Center, a region that shows peculiar environmental conditions. Aims. We present an unbiased spectral survey of one of the most chemically rich hot molecular cores located outside the Galactic Center, in the high-mass star-forming region G31.41+0.31. The aim of this 3mm spectral survey is to identify and characterize the physical parameters of the gas emission in different molecular species, focusing on complex organic molecules. In this first paper, we present the survey and discuss the detection and relative abundances of the three isomers of C2H4O2: methyl formate, glycolaldehyde, and acetic acid. Methods. Observations were carried out with the ALMA interferometer, covering all of band 3 from 84 to 116 GHz (~32 GHz bandwidth) with an angular resolution of 1.2′′ × 1.2′′ (~ 4400 au × 4400 au) and a spectral resolution of ~0.488 MHz (~1.3−1.7 km s−1). The transitions of the three molecules have been analyzed with the software XCLASS to determine the physical parameters of the emitted gas. Results. All three isomers were detected with abundances of (2 ± 0.6) × 10−7, (4.3−8) × 10−8, and (5.0 ± 1.4) × 10−9 for methyl formate, acetic acid, and glycolaldehyde, respectively. Methyl formate and acetic acid abundances are the highest detected up to now, if compared to sources in the literature. The size of the emission varies among the three isomers with acetic acid showing the most compact emission while methyl formate exhibits the most extended emission. Different chemical pathways, involving both grain-surface chemistry and cold or hot gas-phase reactions, have been proposed for the formation of these molecules, but the small number of detections, especially of acetic acid and glycolaldehyde, have made it very difficult to confirm or discard the predictions of the models. The comparison with chemical models in literature suggests the necessity of grain-surface routes for the formation of methyl formate in G31, while for glycolaldehyde both scenarios could be feasible. The proposed grain-surface reaction for acetic acid is not capable of reproducing the observed abundance in this work, while the gas-phase scenario should be further tested, given the large uncertainties involved.

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The formation of glycine and other complex organic molecules in exploding ice mantles

Faraday Discussions ◽

10.1039/c3fd00155e ◽

2014 ◽

Vol 168 ◽

pp. 369-388 ◽

Cited By ~ 6

Author(s):

J. M. C. Rawlings ◽

D. A. Williams ◽

S. Viti ◽

C. Cecchi-Pestellini ◽

W. W. Duley

Keyword(s):

Gas Phase ◽

Molecular Clouds ◽

Organic Molecules ◽

Alternative Mechanism ◽

Hydrogen Atoms ◽

Interstellar Gas ◽

Dark Cloud ◽

Short Period ◽

Molecular Abundances ◽

Complex Organic

Complex Organic Molecules (COMs), such as propylene (CH3CHCH2) and the isomers of C2H4O2 are detected in cold molecular clouds (such as TMC-1) with high fractional abundances (Marcelino et al., Astrophys. J., 2007, 665, L127). The formation mechanism for these species is the subject of intense speculation, as is the possibility of the formation of simple amino acids such as glycine (NH2CH2COOH). At typical dark cloud densities, normal interstellar gas-phase chemistries are inefficient, whilst surface chemistry is at best ill defined and does not easily reproduce the abundance ratios observed in the gas phase. Whatever mechanism(s) is/are operating, it/they must be both efficient at converting a significant fraction of the available carbon budget into COMs, and capable of efficiently returning the COMs to the gas phase. In our previous studies we proposed a complementary, alternative mechanism, in which medium- and large-sized molecules are formed by three-body gas kinetic reactions in the warm high density gas phase. This environment exists, for a very short period of time, after the total sublimation of grain ice mantles in transient co-desorption events. In order to drive the process, rapid and efficient mantle sublimation is required and we have proposed that ice mantle ‘explosions’ can be driven by the catastrophic recombination of trapped hydrogen atoms, and other radicals, in the ice. Repeated cycles of freeze-out and explosion can thus lead to a cumulative molecular enrichment of the interstellar medium. Using existing studies we based our chemical network on simple radical addition, subject to enthalpy and valency restrictions. In this work we have extended the chemistry to include the formation pathways of glycine and other large molecular species that are detected in molecular clouds. We find that the mechanism is capable of explaining the observed molecular abundances and complexity in these sources. We find that the proposed mechanism is easily capable of explaining the large abundances of all three isomers of C2H4O2 that are observationally inferred for star-forming regions. However, the model currently does not provide an obvious explanation for the predominance of methyl formate, suggesting that some refinement to our (very simplistic) chemistry is necessary. The model also predicts the production of glycine at a (lower) abundance level, that is consistent with its marginal detection in astrophysical sources.

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Mapping observations of complex organic molecules around Sagittarius B2 with the ARO 12 m telescope

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3337 ◽

2020 ◽

Vol 492 (1) ◽

pp. 556-565

Author(s):

Juan Li ◽

Junzhi Wang ◽

Haihua Qiao ◽

Donghui Quan ◽

Min Fang ◽

...

Keyword(s):

Spatial Distribution ◽

Gas Phase ◽

Low Temperatures ◽

Organic Molecules ◽

Methyl Formate ◽

Surface Reactions ◽

High Sensitivity ◽

Methyl Amine ◽

Grain Surface ◽

Complex Organic

ABSTRACT We have performed high-sensitivity mapping observations of several complex organic molecules around Sagittarius B2 with the ARO 12 m telescope at 3 mm wavelength. Based on their spatial distribution, molecules can be classified as either ‘extended’, those detected not only in Sgr B2(N) and Sgr B2(M), or ‘compact’, those only detected toward or near Sgr B2(N) and Sgr B2(M). The ‘extended’ molecules include glycolaldehyde (CH2OHCHO), methyl formate (CH3OCHO), formic acid (t-HCOOH), ethanol (C2H5OH) and methyl amine (CH3NH2), while the ‘compact’ molecules include dimethyl ether (CH3OCH3), ethyl cyanide (C2H5CN), and amino acetonitrile (H2NCH2CN). These ‘compact’ molecules are likely produced under strong UV radiation, while the ‘extended’ molecules are likely formed at low temperatures, via gas-phase or grain-surface reactions. The spatial distribution of ‘warm’ CH2OHCHO at 89 GHz differs from the spatial distribution of ‘cold’ CH2OHCHO observed at 13 GHz. We found evidence for an overabundance of CH2OHCHO compared to that expected from the gas-phase model, which indicates that grain-surface reactions are necessary to explain the origin of CH2OHCHO in Sagittarius B2. Grain-surface reactions are also needed to explain the correlation between the abundances of ‘cold’ CH2OHCHO and C2H5OH. These results demonstrate the importance of grain-surface chemistry in the production of complex organic molecules.

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Complex Organic Molecules Formation in Space Through Gas Phase Reactions: A Theoretical Approach

The Astrophysical Journal ◽

10.3847/1538-4357/aa5ca4 ◽

2017 ◽

Vol 836 (2) ◽

pp. 240 ◽

Cited By ~ 1

Author(s):

Pilar Redondo ◽

Carmen Barrientos ◽

Antonio Largo

Keyword(s):

Gas Phase ◽

Theoretical Approach ◽

Organic Molecules ◽

Gas Phase Reactions ◽

Complex Organic

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Surface Reactions in Interstellar Space

Highlights of Astronomy ◽

10.1017/s1539299600012818 ◽

2002 ◽

Vol 12 ◽

pp. 55-57 ◽

Cited By ~ 1

Author(s):

Eric Herbst

Keyword(s):

Surface Chemistry ◽

Gas Phase ◽

Condensed Phase ◽

Current Knowledge ◽

Surface Reactions ◽

Future Research ◽

Interstellar Space ◽

Interstellar Molecules ◽

Grain Surface

AbstractIt is impossible to explain the abundances of some gas-phase and most condensed-phase interstellar molecules without the use of grain chemistry. Nevertheless, grain-surface chemistry is relatively poorly understood for a variety of reasons. Our current knowledge of this chemistry and its use in interstellar models is discussed along with specific needs for future research.

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