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

2014 ◽  
Vol 168 ◽  
pp. 369-388 ◽  
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.

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

2014 ◽  
Vol 168 ◽  
pp. 389-421 ◽  
Author(s):  
Catherine Walsh ◽  
Eric Herbst ◽  
Hideko Nomura ◽  
T. J. Millar ◽  
Susanna Widicus Weaver
Keyword(s):  
Surface Chemistry ◽  
Gas Phase ◽  
Organic Molecules ◽  
Molecular Layer ◽  
Accretion Flow ◽  
Chemical Complexity ◽  
Outer Disk ◽  
Molecular Abundances ◽  
Grain Surface ◽  
Complex Organic

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.

Gas-phase reactivity of CH3OH+OH down to 11.7 K: Astrophysical implications

2019 ◽  
Vol 15 (S350) ◽  
pp. 365-367
Author(s):  
Antonio J. Ocaña ◽  
Sergio Blázquez ◽  
Daniel González ◽  
Alexey Potapov ◽  
Bernabé Ballesteros ◽  
...  
Keyword(s):  
Gas Phase ◽  
Molecular Clouds ◽  
Organic Molecules ◽  
Rate Coefficients ◽  
Reaction Networks ◽  
Oh Radicals ◽  
Temperature Reaction ◽  
Starting Point ◽  
Prebiotic Molecules ◽  
Complex Organic

AbstractMethanol (CH3OH) and hydroxyl (OH) radicals are two species abundant in cold and dense molecular clouds which are important for the chemistry of the interstellar medium (ISM). CH3OH is a well-known starting point for the formation of more complex organic molecules (COMs) in these molecular clouds. Thus, the reactivity of CH3OH in the gas-phase with OH may play a crucial role in the formation of species as complex as prebiotic molecules in the ISM and reliable rate coefficients should be used in astrochemical models describing low temperature reaction networks.

scholarly journals Aldehydes and sugars from evolved precometary ice analogs: Importance of ices in astrochemical and prebiotic evolution

2015 ◽  
Vol 112 (4) ◽  
pp. 965-970 ◽  
Author(s):  
Pierre de Marcellus ◽  
Cornelia Meinert ◽  
Iuliia Myrgorodska ◽  
Laurent Nahon ◽  
Thomas Buhse ◽  
...  
Keyword(s):  
Gas Phase ◽  
Molecular Clouds ◽  
Room Temperature ◽  
Laboratory Experiments ◽  
Organic Residue ◽  
Organic Residues ◽  
Flight Mass Spectrometry ◽  
The Earth ◽  
Planetary Environment ◽  
Complex Organic

Evolved interstellar ices observed in dense protostellar molecular clouds may arguably be considered as part of precometary materials that will later fall on primitive telluric planets, bringing a wealth of complex organic compounds. In our laboratory, experiments reproducing the photo/thermochemical evolution of these ices are routinely performed. Following previous amino acid identifications in the resulting room temperature organic residues, we have searched for a different family of molecules of potential prebiotic interest. Using multidimensional gas chromatography coupled to time-of-flight mass spectrometry, we have detected 10 aldehydes, including the sugar-related glycolaldehyde and glyceraldehyde—two species considered as key prebiotic intermediates in the first steps toward the synthesis of ribonucleotides in a planetary environment. The presence of ammonia in water and methanol ice mixtures appears essential for the recovery of these aldehydes in the refractory organic residue at room temperature, although these products are free of nitrogen. We finally point out the importance of detecting aldehydes and sugars in extraterrestrial environments, in the gas phase of hot molecular clouds, and, more importantly, in comets and in primitive meteorites that have most probably seeded the Earth with organic material as early as 4.2 billion years ago.

scholarly journals Laboratory data in support of JWST observations of interstellar ices

2019 ◽  
Vol 15 (S350) ◽  
pp. 420-421
Author(s):  
Marina G. Rachid ◽  
Jeroen Terwisscha van Scheltinga ◽  
Daniël Koletzki ◽  
Giulia Marcandalli ◽  
Ewine F. van Dishoeck ◽  
...  
Keyword(s):  
Solid State ◽  
Gas Phase ◽  
Organic Molecules ◽  
Methyl Formate ◽  
Laboratory Data ◽  
Protoplanetary Disks ◽  
Theoretical Studies ◽  
James Webb Space Telescope ◽  
Complex Organic ◽  
Experimental And Theoretical Studies

AbstractExperimental and theoretical studies have shown that Complex Organic Molecules (COMs) can be formed on icy dusty grains in molecular clouds and protoplanetary disks. The number of astronomical detections of solid COMs, however, is very limited. With the upcoming launch of the James Webb Space Telescope (JWST) this should change, but in order to identify solid state features of COMs, accurate laboratory data are needed. Here we present high resolution (0.5 cm–1) infrared ice spectra of acetone (C3H6O) and methyl formate (HCOOCH3), two molecules already identified in astronomical gas phase surveys, whose interstellar synthesis is expected to follow solid state pathways.

scholarly journals Infrared spectra of complex organic molecules in astronomically relevant ice matrices

2018 ◽  
Vol 611 ◽  
pp. A35 ◽  
Author(s):  
J. Terwisscha van Scheltinga ◽  
N. F. W. Ligterink ◽  
A. C. A. Boogert ◽  
E. F. van Dishoeck ◽  
H. Linnartz
Keyword(s):  
Gas Phase ◽  
Dimethyl Ether ◽  
Organic Molecules ◽  
Laboratory Data ◽  
Laboratory Studies ◽  
Astronomical Data ◽  
Astronomical Observations ◽  
Circumstellar Gas ◽  
Complex Organic ◽  
Recent Laboratory

Context. The number of identified complex organic molecules (COMs) in inter- and circumstellar gas-phase environments is steadily increasing. Recent laboratory studies show that many such species form on icy dust grains. At present only smaller molecular species have been directly identified in space in the solid state. Accurate spectroscopic laboratory data of frozen COMs, embedded in ice matrices containing ingredients related to their formation scheme, are still largely lacking.Aim. This work provides infrared reference spectra of acetaldehyde (CH3CHO), ethanol (CH3CH2OH), and dimethyl ether (CH3OCH3) recorded in a variety of ice environments and for astronomically relevant temperatures, as needed to guide or interpret astronomical observations, specifically for upcoming James Webb Space Telescope observations.Methods. Fourier transform transmission spectroscopy (500–4000 cm−1/20–2.5 μm, 1.0 cm−1 resolution) was used to investigate solid acetaldehyde, ethanol and dimethyl ether, pure or mixed with water, CO, methanol, or CO:methanol. These species were deposited on a cryogenically cooled infrared transmissive window at 15 K. A heating ramp was applied, during which IR spectra were recorded until all ice constituents were thermally desorbed.Results. We present a large number of reference spectra that can be compared with astronomical data. Accurate band positions and band widths are provided for the studied ice mixtures and temperatures. Special efforts have been put into those bands of each molecule that are best suited for identification. For acetaldehyde the 7.427 and 5.803 μm bands are recommended, for ethanol the 11.36 and 7.240 μm bands are good candidates, and for dimethyl ether bands at 9.141 and 8.011 μm can be used. All spectra are publicly available in the Leiden Database for Ice.

On The Nature of Interstellar Organic Chemistry

1997 ◽  
Vol 161 ◽  
pp. 89-96 ◽  
Author(s):  
Steven B. Charnley
Keyword(s):  
Gas Phase ◽  
Molecular Clouds ◽  
Organic Molecules ◽  
Single Atom ◽  
Addition Reactions ◽  
Mass Star ◽  
Quantum Tunnelling ◽  
Dark Clouds ◽  
Murchison Meteorite ◽  
Low Mass

AbstractA theory for the origin of all organic molecules observed in regions of massive and low-mass star formation, as well as in dark molecular clouds is described. On dust grains, single atom addition reactions and stability of the intermediate radicals, mechanisms similar to those believed to form the organic component of the Murchison meteorite, lead to a very limited number of mantle compositions depending upon the degree of hydrogenation. The key step in the theory is the formation of the formyl radical by H atom addition (by quantum tunnelling) to CO. Subsequent H atom additions lead to formaldehyde and methanol, as previously suggested; C, N, and O atoms can also undergo additions to HCO. For increasing hydrogenation, the mantle types include one in which there is little contribution from formyl-initiated chemistry; one in which an acetylenic chain develops through C atom additions; and others where the acetylenic chain is increasingly hydrogenated to form aldehydes and alcohols. Following evaporation of grain mantles, such as occurs in protostellar «hot cores», these molecules can form new organics, for example, by alkyl cation transfer from alcohols. In dark clouds, different mantles lead to different gas phase organics. This scenario accounts naturally for the formation of many interstellar organics for which none presently exists, predicts observable correlations between specific interstellar molecules, indicates the presence of many new organic molecules and why several others are not observed.

scholarly journals Comparing ice composition in dark molecular clouds

2008 ◽  
Vol 4 (S251) ◽  
pp. 47-48 ◽  
Author(s):  
C. Knez ◽  
M. Moore ◽  
S. Travis ◽  
R. Ferrante ◽  
J. Chiar ◽  
...  
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Organic Molecules ◽  
Dark Cloud ◽  
Preliminary Results ◽  
Level Of Activity ◽  
Star Formation Activity

AbstractWe present 5–20 μm Spitzer/IRS spectroscopy toward stars behind dark molecular clouds. We present preliminary results from the Serpens dark cloud to show the variation between environments within a cloud. We are surveying 3 clouds with varying levels of star formation activity. Serpens has the highest level of activity from our 3 clouds. We show that location as well extinction can cause variations in ice composition. We also find that some lines of sight contain organic molecules such as methane and methanol, and the first detection of acetylene ice in the interstellar medium. We believe the high extinction lines of sight have been enriched by star formation activity near those lines of sight.

scholarly journals Dust and molecules in extra-galactic planetary nebulae

2015 ◽  
Vol 11 (A29B) ◽  
Author(s):  
D. A. García-Hernández
Keyword(s):  
Solid State ◽  
Gas Phase ◽  
Organic Molecules ◽  
Local Group ◽  
Planetary Nebulae ◽  
Circumstellar Envelopes ◽  
The Galaxy ◽  
Models Comparison ◽  
Polycyclic Aromatic ◽  
Complex Organic

AbstractExtra-galactic planetary nebulae (PNe) permit the study of dust and molecules in metallicity environments other than the Galaxy. Their known distances lower the number of free parameters in the observations vs. models comparison, providing strong constraints on the gas-phase and solid-state astrochemistry models. Observations of PNe in the Galaxy and other Local Group galaxies such as the Magellanic Clouds (MC) provide evidence that metallicity affects the production of dust as well as the formation of complex organic molecules and inorganic solid-state compounds in their circumstellar envelopes. In particular, the lower metallicity MC environments seem to be less favorable to dust production and the frequency of carbonaceous dust features and complex fullerene molecules is generally higher with decreasing metallicity. Here, I present an observational review of the dust and molecular content in extra-galactic PNe as compared to their higher metallicity Galactic counterparts. A special attention is given to the level of dust processing and the formation of complex organic molecules (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene precursors) depending on metallicity.

scholarly journals Non-thermal desorption of complex organic molecules

2020 ◽  
Vol 634 ◽  
pp. A103
Author(s):  
E. Dartois ◽  
M. Chabot ◽  
A. Bacmann ◽  
P. Boduch ◽  
A. Domaracka ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Gas Phase ◽  
Organic Molecules ◽  
Solid Phase ◽  
Bulk Composition ◽  
Cosmic Ray ◽  
Water Ice ◽  
Sputtering Yield ◽  
Sputtering Yields ◽  
Complex Organic

Aims. Methanol ice is embedded in interstellar ice mantles present in dense molecular clouds. We aim to measure the sputtering efficiencies starting from different ice mantles of varying compositions experimentally, in order to evaluate their potential impact on astrochemical models. The sputtering yields of complex organic molecules is of particular interest, since few mechanisms are efficient enough to induce a significant feedback to the gas phase. Methods. We irradiated ice film mixtures made of methanol and carbon dioxide of varying ratios with swift heavy ions in the electronic sputtering regime. We monitored the evolution of the infrared spectra as well as the species released to the gas phase with a mass spectrometer. Methanol (12C) and isotopically labelled 13C-methanol were used to remove any ambiguity on the measured irradiation products. Results. The sputtering of methanol embedded in carbon dioxide ice is an efficient process leading to the ejection of intact methanol in the gas phase. We establish that when methanol is embedded in a carbon-dioxide-rich mantle exposed to cosmic rays, a significant fraction (0.2–0.3 in this work) is sputtered as intact molecules. The sputtered fraction follows the time-dependent bulk composition of the ice mantle, the latter evolving with time due to the radiolysis-induced evolution of the bulk. If methanol is embedded in a carbon dioxide ice matrix, as the analyses of the spectral shape of the CO2 bending mode observations in some lines of sight suggest, the overall methanol sputtering yield is higher than if embedded in a water ice mantle. The sputtering is increased by a factor close to the dominant ice matrix sputtering yield, which is about six times higher for pure carbon dioxide ice when compared to water ice. These experiments are further constraining the cosmic-ray-induced ice mantle sputtering mechanisms important role in the gas-phase release of complex organic molecules from the interstellar solid phase.

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