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).

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 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.

scholarly journals Interstellar Dust and the Organic Inventories of Early Solar Systems

2004 ◽  
Vol 213 ◽  
pp. 163-168
Author(s):  
D. C. B. Whittet
Keyword(s):  
Solar System ◽  
Interstellar Dust ◽  
Organic Molecules ◽  
Solar Nebula ◽  
Chemical Elements ◽  
Interstellar Space ◽  
Complex Molecules ◽  
Solar Systems ◽  
Physical Conditions ◽  
Interstellar Dust Grains

Interstellar dust grains are vectors for cosmic carbon and other biogenic chemical elements. They deliver carbon to protoplanetary disks in various refractory phases (amorphous, graphitic, etc.), and they are coated with icy mantles that contain organic molecules and water. The nature of the organics present in and on the dust appears to be closely related to physical conditions. Complex molecules may be synthesized when simple ices are irradiated. Astronomical observations show that this occurs in the vicinity of certain massive protostars, but it is not known whether our Solar System formed in such a region. Organic matter does not survive cycling though diffuse regions of interstellar space; any organics delivered to the early Earth must have originated in the parent molecular cloud, or in the solar nebula itself. A key question is thus identified: What was the star-formation environment of the Solar System? Possible constraints are briefly discussed.

scholarly journals Properties of the circumgalactic medium in simulations compared to observations

2018 ◽  
Vol 609 ◽  
pp. A66 ◽  
Author(s):  
R. E. G. Machado ◽  
P. B. Tissera ◽  
G. B. Lima Neto ◽  
L. Sodré
Keyword(s):  
Gas Phase ◽  
Chemical Elements ◽  
Star Forming ◽  
Physical Conditions ◽  
Cosmological Context ◽  
Circumgalactic Medium ◽  
Hydrodynamical Simulations ◽  
Stellar Masses ◽  
Lower Limits ◽  
Supernova Feedback

Context. Galaxies are surrounded by extended gaseous halos that store significant fractions of chemical elements. These are syntethized by the stellar populations and later ejected into the circumgalactic medium (CGM) by different mechanism, of which supernova feedback is considered one of the most relevant. Aims. We aim to explore the properties of this metal reservoir surrounding star-forming galaxies in a cosmological context aiming to investigate the chemical loop between galaxies and their CGM, and the ability of the subgrid models to reproduce observational results. Methods. Using cosmological hydrodynamical simulations, we have analysed the gas-phase chemical contents of galaxies with stellar masses in the range 109−1011 M⊙. We estimated the fractions of metals stored in the different CGM phases, and the predicted O vi and Si iii column densities within the virial radius. Results. We find roughly 107 M⊙ of oxygen in the CGM of simulated galaxies having M⋆ ~ 1010 M⊙, in fair agreement with the lower limits imposed by observations. The Moxy is found to correlate with M⋆, at odds with current observational trends but in agreement with other numerical results. The estimated profiles of O vi column density reveal a substantial shortage of that ion, whereas Si iii, which probes the cool phase, is overpredicted. Nevertheless, the radial dependences of both ions follow the respective observed profiles. The analysis of the relative contributions of both ions from the hot, warm and cool phases suggests that the warm gas (105 K < T < 106 K) should be more abundant in order to bridge the mismatch with the observations, or alternatively, that more metals should be stored in this gas-phase. These discrepancies provide important information to improve the subgrid physics models. Our findings show clearly the importance of tracking more than one chemical element and the difficulty of simultaneously satisfying the observables that trace the circumgalactic gas at different physical conditions. Additionally, we find that the X-ray coronae around the simulated galaxies have luminosities and temperatures in decent agreement with the available observational estimates.

Calixarene receptors of environmentally hazardous and biorelevant molecules and ions

2008 ◽  
Vol 80 (7) ◽  
pp. 1449-1458 ◽  
Author(s):  
Vitaly I. Kalchenko
Keyword(s):  
Drug Design ◽  
Gas Phase ◽  
Crystalline State ◽  
Rational Design ◽  
Organic Molecules ◽  
Supramolecular Complexes

In the paper, a report on the rational design of the calixarene receptors bearing ligating, H-donor, H-acceptor fragments at the wide and/or narrow rim of the macrocycle is presented. The calixarenes form supramolecular complexes with various cations, anions, organic molecules, and biomolecules in solution, in the crystalline state and even in the gas phase. The calixarenes or their complexes can be used as materials for radionuclide extraction, construction of chemosensors, and drug design.

scholarly journals Molecules in nearby and primordial supernovae

2008 ◽  
Vol 4 (S251) ◽  
pp. 221-226
Author(s):  
Isabelle Cherchneff ◽  
Simon Lilly
Keyword(s):  
Gas Phase ◽  
Early Universe ◽  
Organic Molecules ◽  
Molecular Form ◽  
Chemical Kinetic ◽  
Kinetic Approach ◽  
Dust Formation ◽  
Core Collapse ◽  
Chemical Models ◽  
Upper Limits

AbstractWe present new chemical models of supernova (SN) ejecta based on a chemical kinetic approach. We focus on the formation of inorganic and organic molecules including gas phase dust precursors, and consider zero-metallicity progenitor, massive supernovae and nearby core-collapse supernovae such as SN1987A. We find that both types are forming large amounts of molecules in their ejecta at times as early as 200 days after explosion. Upper limits on the dust formation budget are derived. Our results on dust precursors do not agree with existing studies on dust condensation in SN ejecta. We conclude that PMSNe could be the first non-primodial molecule providers in the early universe, ejecting up to 34% of their progenitor mass under molecular form to the pristine, local gas.

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