scholarly journals Gas-phase formation of acetaldehyde: review and new theoretical computations

2020 ◽  
Vol 499 (4) ◽  
pp. 5547-5561
Author(s):  
Fanny Vazart ◽  
Cecilia Ceccarelli ◽  
Nadia Balucani ◽  
Eleonora Bianchi ◽  
Dimitrios Skouteris
Keyword(s):  
Gas Phase ◽  
Phase Formation ◽  
Organic Molecules ◽  
Phase Reaction ◽  
Data Bases ◽  
Major Interest ◽  
Complex Organic ◽  
Formation Paths ◽  
Density Regime ◽  
Reaction Routes

ABSTRACT Among all the interstellar complex organic molecules, acetaldehyde is one of the most widely detected species. The question of its formation route(s) is, therefore, of a major interest regarding astrochemical models. In this paper, we provide an extensive review of the gas-phase formation paths that were, or are, reported in the literature and the major astrochemical data bases. Four different gas-phase formation routes stand out : (1) CH3OCH3  + H+/CH3CHOH+  + e−, (2) C2H5  + O(3P), (3) CH3OH  + CH, and (4) CH3CH2OH  + OH/CH3CHOH  + O(3P). Paths (2) and (3) were not studied neither via laboratory nor theoretical works in the low temperature and density regime valid for the interstellar medium (ISM). Thus, we carried out new accurate quantum chemistry computations. A theoretical kinetics study at low temperatures (7 ÷ 300 K), adopting the Rice–Ramsperger–Kassel–Marcus scheme, was also performed. We confirm that reaction (2) is efficient in forming acetaldehyde in the 7–300 temperature range (α  = 1.21 × 10−10 cm3 s−1 and β = 0.16). On the contrary, our new computations disprove the formation of acetaldehyde through reaction (3) (α = 1.84 ÷ 0.67 × 10−13 cm3 s−1 and β = −0.07 ÷ −0.95). Path (1) was showed to be inefficient too by recent computations, while path (4) was formerly considered for glycolaldehyde formation, having acetaldehyde as a byproduct. In conclusions, of the four above paths, only two, the (2) and (4), are potentially efficient gas-phase reaction routes for the formation of acetaldehyde and we encourage astrochemical modellers to consider only them. Comparison with astronomical observations suggests that path (4) may actually play the major role.

Gas phase reaction kinetics of complex organic molecules at temperatures of the interstellar medium: The OH + CH3OH case

2019 ◽  
Vol 15 (S350) ◽  
pp. 35-40 ◽  
Author(s):  
André Canosa
Keyword(s):  
Interstellar Medium ◽  
Reaction Kinetics ◽  
Gas Phase ◽  
Organic Molecules ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Potential Impact ◽  
Kinetics Of ◽  
Complex Organic

AbstractRecent experimental and theoretical works concerning gas-phase radical-neutral reactions involving Complex Organic Molecules are reviewed in the context of cold interstellar objects with a special emphasis on the OH + CH3OH reaction and its potential impact on the formation of CH3O.

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.

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.

scholarly journals Laboratory constraints on ice formation, restructuring and desorption

2015 ◽  
Vol 11 (A29A) ◽  
pp. 309-312
Author(s):  
Karin I. Öberg
Keyword(s):  
Gas Phase ◽  
Chemical Reactions ◽  
Organic Molecules ◽  
Protoplanetary Disks ◽  
Ice Formation ◽  
Circumstellar Dust ◽  
Dust Grains ◽  
Complex Molecules ◽  
Detailed Understanding ◽  
Complex Organic

AbstractIces form on the surfaces of interstellar and circumstellar dust grains though freeze-out of molecules and atoms from the gas-phase followed by chemical reactions. The composition, chemistry, structure and desorption properties of these ices regulate two important aspects of planet formation: the locations of major condensation fronts in protoplanetary disks (i.e. snow lines) and the formation efficiencies of complex organic molecules in astrophysical environments. The latter regulates the availability of prebiotic material on nascent planets. With ALMA it is possible to directly observe both (CO) snowlines and complex organics in protoplanetary disks. The interpretation of these observations requires a detailed understanding of the fundamental ice processes that regulate the build-up, evolution and desorption of icy grain mantles. This proceeding reviews how experiments on thermal CO and N2 ice desorption, UV photodesorption of CO ice, and CO diffusion in H2O ice have been used to guide and interpret astrochemical observations of snowlines and complex molecules.

scholarly journals Chemical complexity in the Horsehead photodissociation region

2014 ◽  
Vol 168 ◽  
pp. 103-127 ◽  
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.

scholarly journals Formation of alcohols on ice surfaces

2008 ◽  
Vol 4 (S251) ◽  
pp. 377-382
Author(s):  
H. M. Cuppen ◽  
G. W. Fuchs ◽  
S. Ioppolo ◽  
S. E. Bisschop ◽  
K. I. Öberg ◽  
...  
Keyword(s):  
Gas Phase ◽  
Organic Molecules ◽  
Co Hydrogenation ◽  
Formation Rate ◽  
Physical Processes ◽  
Complex Molecules ◽  
Physical Conditions ◽  
Ethanol Formation ◽  
Hydrogenation Reactions ◽  
Reaction Routes

AbstractAs the number of detections of complex molecules keeps increasing, answering the question about their formation becomes more pressing. Many of the saturated organic molecules are found to have a very low gas phase formation rate and are therefore thought to be formed on the icy surfaces of dust grains. In the Sackler Laboratory for Astrophysics we started a systematic study of the surface reaction routes that have been suggested over the years. Here we present the experimental results on the formation of methanol and ethanol by hydrogenation reactions of carbon monoxide and acetaldehyde ice. Computer simulations of the surface processes under similar conditions using the continuous-time random-walk Monte Carlo technique reveal some of the underlying physical processes. A better understanding of the physical conditions in which these molecules are formed can help in the interpretation of the observational results. The CO hydrogenation results will appear in detail in Fuchs et al. (2008). For more details on ethanol formation we refer to Bisschop et al. (2007).

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