scholarly journals Thermal desorption of water ice in the interstellar medium

2001 ◽  
Vol 327 (4) ◽  
pp. 1165-1172 ◽  
Author(s):  
H. J. Fraser ◽  
M. P. Collings ◽  
M. R. S. McCoustra ◽  
D. A. Williams
Keyword(s):  
Interstellar Medium ◽  
Thermal Desorption ◽  
Water Ice

scholarly journals Computational studies into urea formation in the interstellar medium

2020 ◽  
Vol 497 (4) ◽  
pp. 5413-5420
Author(s):  
Eren C S Slate ◽  
Rory Barker ◽  
Ryan T Euesden ◽  
Max R Revels ◽  
Anthony J H M Meijer
Keyword(s):  
Interstellar Medium ◽  
Computational Methods ◽  
Radical Reaction ◽  
Closed Shell ◽  
Computational Studies ◽  
Water Ice ◽  
Charged Species ◽  
Ice Shell ◽  
Partial Water

ABSTRACT Formation routes, involving closed shell, radical, and charged species for urea, have been studied using computational methods to probe their feasibility in the interstellar medium. All reactions involving closed shell species were found to have prohibitive barriers. The radical–radical reaction possesses a barrier of only 4 kJ mol−1, which could be surmountable. A charged species based route was also investigated. A barrier of only 8 kJ mol−1 was found in that case, when a partial water ice shell was included.

scholarly journals Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

2019 ◽  
Vol 15 (S350) ◽  
pp. 370-371
Author(s):  
Henda Chaabouni ◽  
Stephan Diana ◽  
Thanh Nguyen
Keyword(s):  
Energy Distribution ◽  
Thermal Desorption ◽  
Interstellar Dust ◽  
Binding Energies ◽  
Desorption Energy ◽  
Exponential Factor ◽  
Water Ice ◽  
Ice Surface ◽  
Crystalline Water ◽  
Best Fit

AbstractThermal desorption experiments of Formamide (NH2CHO) and methylamine (CH3NH2) were performed in LERMA-Cergy laboratory to determine the values of the desorption energies of formamide and methylamine from analogues of interstellar dust grain surfaces, and to understand their interaction with water ice. We found that more than 95 % of solid NH2CHO diffuses through the np-ASW ice surface towards the graphitic substrate, and is released into the gas phase with a desorption energy distribution Edes = (7460 – 9380) K, measured with the best-fit pre-exponential factor A=1018 s-1. Whereas, the desorption energy distribution of methylamine from the np-ASW ice surface (Edes =3850-8420 K) is measured with the best-fit pre-exponential factor A=1012s-1. A fraction of solid methylamine, of about 0.15 monolayer diffuses through the water ice surface towards the HOPG substrate, and desorbs later, with higher binding energies (5050-8420 K), which exceed that of the crystalline water ice (Edes =4930 K), calculated with the same pre-exponential factor A=1012 s-1.

Quantum chemical study on the formation of isopropyl cyanide and its linear isomer in the interstellar medium

2020 ◽  
pp. 1-11
Author(s):  
Keshav Kumar Singh ◽  
Poonam Tandon ◽  
Alka Misra ◽  
Shivani ◽  
Manisha Yadav ◽  
...  
Keyword(s):  
Amino Acids ◽  
Interstellar Medium ◽  
Gas Phase ◽  
Quantum Chemical ◽  
Density Functional ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Dark Cloud ◽  
Water Ice ◽  
Hydrocarbon Radicals

Abstract The formation mechanism of linear and isopropyl cyanide (hereafter n-PrCN and i-PrCN, respectively) in the interstellar medium (ISM) has been proposed from the reaction between some previously detected small cyanides/cyanide radicals and hydrocarbons/hydrocarbon radicals. n-PrCN and i-PrCN are nitriles therefore, they can be precursors of amino acids via Strecker synthesis. The chemistry of i-PrCN is especially important since it is the first and only branched molecule in ISM, hence, it could be a precursor of branched amino acids such as leucine, isoleucine, etc. Therefore, both n-PrCN and i-PrCN have significant astrobiological importance. To study the formation of n-PrCN and i-PrCN in ISM, quantum chemical calculations have been performed using density functional theory at the MP2/6-311++G(2d,p)//M062X/6-311+G(2d,p) level. All the proposed reactions have been studied in the gas phase and the interstellar water ice. It is found that reactions of small cyanide with hydrocarbon radicals result in the formation of either large cyanide radicals or ethyl and vinyl cyanide, both of which are very important prebiotic interstellar species. They subsequently react with the radicals CH2 and CH3 to yield n-PrCN and i-PrCN. The proposed reactions are efficient in the hot cores of SgrB2 (N) (where both n-PrCN and i-PrCN were detected) due to either being barrierless or due to the presence of a permeable entrance barrier. However, the formation of n-PrCN and i-PrCN from the ethyl and vinyl cyanide always has an entrance barrier impermeable in the dark cloud; therefore, our proposed pathways are inefficient in the deep regions of molecular clouds. It is also observed that ethyl and vinyl cyanide serve as direct precursors to n-PrCN and i-PrCN and their abundance in ISM is directly related to the abundance of both isomers of propyl cyanide in ISM. In all the cases, reactions in the ice have smaller barriers compared to their gas-phase counterparts.

scholarly journals The quest of chirality in the interstellar medium

2020 ◽  
Vol 633 ◽  
pp. A49
Author(s):  
Y. Ellinger ◽  
F. Pauzat ◽  
A. Markovits ◽  
A. Allaire ◽  
J.-C. Guillemin
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
Propylene Oxide ◽  
Density Functional ◽  
Energy Scale ◽  
Potential Candidate ◽  
Structural Constraints ◽  
Water Ice ◽  
Rotational Spectra ◽  
Complex Organic Molecule

Context. All but one complex organic molecule (COM) detected so far in the interstellar medium (ISM) are achiral; propylene oxide (c-C2H3O)-CH3 is the only exception to this. Finding other chiral species is a priority for astrobiology to progress in the understanding of the emergence of life. Whatever the conditions of their formation, i.e., gas phase or grain chemistry, the detection relies on rotational spectra. This means that, if adsorbed after formation in the gas phase or directly formed on the icy grains, these COMs must escape in the gas phase as free flyers to be detectable. Aims. Learning the lesson drawn from the only observation of a chiral compound and considering the structural constraints imposed to a molecule to be chiral, we look at what species could satisfy these conditions and be potential targets for a radio astronomy search in the ISM gas phase. Methods. This question was addressed by combining two complementary approaches that rely on density functional theory. The structure, energetics, and spectroscopic parameters of each potential candidate were determined using molecular calculations. The propensity for a molecule to remain trapped on the ice coating of the grains was evaluated by numerical simulations making use of a solid state periodic model. Results. Replacing the -CH3 group on rigid propylene oxide by -CN, -CCH, -NH2, -OH, or -HCO gives oxirane daughter molecules whose adsorption energies divide into two classes: below and above the adsorption energy of H2O on solid water-ice ~13.5 kcal mol−1. Conclusions. The best chiral candidate would be a rigid molecule for an easier determination of its radio spectra. This molecule would be composed of a central carbon linked to one hydrogen and three different chemical groups as simple as possible. If not the most stable isomer, this candidate should be as close as possible on the energy scale, possess a significant dipole moment, and be less strongly attached to the ice than H2O itself.

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 Does Processing or Formation of Water Ice Mantles Affect the Capacity of Nanosilicates to Be the Source of Anomalous Microwave Emission?

2021 ◽  
Vol 8 ◽  
Author(s):  
Joan Mariñoso Guiu ◽  
Stefano Ferrero ◽  
Antonio Macià Escatllar ◽  
Albert Rimola ◽  
Stefan T. Bromley
Keyword(s):  
Dipole Moment ◽  
Interstellar Medium ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Ice Nucleation ◽  
Microwave Emission ◽  
Molecular Water ◽  
60 Ghz ◽  
Frequency Range ◽  
Water Ice

Anomalous microwave emission (AME) is detected in many astrophysical environments as a foreground feature typically peaking between 20–30 GHz and extending over a 10–60 GHz range. One of the leading candidates for the source of AME is small spinning dust grains. Such grains should be very small (approx. ≤1 nm diameter) in order for the rotational emission to fall within the observed frequency range. In addition, these nanosized grains should possess a significant dipole moment to account for the observed emissivities. These constraints have been shown to be compatible with spinning bare nanosilicate clusters, assuming that ∼1% of the total Si mass budget is held in these ultrasmall grains. Silicate dust can be hydroxylated by processing in the interstellar medium and is generally known to provide seeds for molecular water ice nucleation in denser regions. Herein, we use quantum chemical calculations to investigate how the dipole moment of Mg-rich pyroxenic (MgSiO3) nanoclusters is affected by both accretion of molecular water and dissociative hydration. Our work thus provides an indication of how the formation of water ice mantles is likely to affect the capacity of nanosilicates to generate AME.

scholarly journals Formation, destruction and chemical influences of water ice: A review of recent laboratory results

2015 ◽  
Vol 11 (A29B) ◽  
pp. 385-389
Author(s):  
Karin I. Öberg
Keyword(s):  
Interstellar Medium ◽  
Laboratory Experiments ◽  
Planet Formation ◽  
Abundant Species ◽  
Current Understanding ◽  
Addition Reactions ◽  
Water Ice ◽  
Laboratory Results ◽  
Recent Laboratory

AbstractWater ice is the dominant constituent of icy grain mantles in the interstellar medium, and as such one of the most abundant species during all stages of star and planet formation. Its formation through atom addition reactions on grain surfaces, its destruction through different desorption channels, and its influence on the chemistry and desorption efficiencies of other species in icy grain mantles have all been the objects of intense study. This contribution reviews our current understanding of these processes, and the laboratory experiments that have been instrumental in establishing the existing paradigm.

C2H5NO Isomers: from Acetamide to1,2-Oxazetidine and Beyond

2021 ◽  
Author(s):  
John Simmie
Keyword(s):  
Machine Learning ◽  
Interstellar Medium ◽  
Catalytic Reaction ◽  
Chemical Bonding ◽  
Energy Barrier ◽  
Current Debate ◽  
Molecular Formula ◽  
Water Addition ◽  
Water Ice ◽  
The Subject

This work documents the properties of a number of isomers of molecular formula C2H5NO from the most stable, acetamide, through 1,2-oxazetidine and including even higher energy species largely of a dipolar nature. Only two of the isomers have been detected in emissions from the interstellar medium (ISM); possible further candidates are identifi�ed and the likelihood of their being detectable are considered. In general hardly any of these compounds have featured in the existing chemical literature so this work represents an important contribution extending the canon of chemical bonding which can contribute to machine-learning | providing a more exacting test of AI applications. The presence of acetamide, CH3C(O)NH2, is the subject of current debate with no clear and obvious paths to its formation; it is shown that a 1,3[H]-transfer from (E,Z ) ethanimidic acid, CH3C(OH){{NH, is feasible in spite of an energy barrier of 130 kJ/mol. It is speculated that the imidic acid can itself be formed from abundant precursors, H2O and CH3C{{{N, in an acid-induced, water addition, auto-catalytic reaction on water-ice grains.

Sign in / Sign up

Export Citation Format

Share Document