Thermal formation of hydroxynitriles, precursors of hydroxyacids in astrophysical ice analogs: Acetone ((CH3)2CO) and hydrogen cyanide (HCN) reactivity (original) (raw)
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Monthly Notices of the Royal Astronomical Society, 2014
Water is the most abundant compound in interstellar and cometary ices. Laboratory experiments on ice analogues have shown that water has a great influence on the chemical activity of these ices. In this study, we investigated the reactivity of acetone-ammonia ices, showing that water is an essential component in chemical reactions with high activation energies. In a water-free binary ice, acetone and ammonia do not react due to high activation energy, as the reactants desorb before reacting (at 120 and 140 K, respectively). By contrast, our study shows that under experimental conditions of ∼150 K, this reaction does occur in the presence of water. Here, water traps reactants in the solid phase above their desorption temperatures, allowing them to gather thermal energy as the reaction proceeds. Using infrared spectroscopy and mass spectrometry associated with isotopic labelling, as well as quantum chemical calculations, 2-aminopropan-2-ol (2 HN-C(CH 3) 2-OH) was identified as the acetone-ammonia reaction product. The formation of this product may represent the first step towards formation of 2-aminoisobutyric acid (AIB) in the Strecker synthesis. The activation energy for the formation of 2-aminopropan-2-ol was measured to be 42 ± 3 kJ mol −1 , while its desorption energy equalled 61.3 ± 0.1 kJ mol −1. Our work demonstrates that astrophysical water, rather than being a non-thermally reactive species, is crucial for the evolution of complex chemistry occurring in the Universe.
Kinetics and Mechanisms of the Acid-Base Reaction Between NH3AND Hcooh in Interstellar Ice Analogs
The Astrophysical Journal, 2016
Interstellar complex organic molecules are commonly observed during star formation, and are proposed to form through radical chemistry in icy grain mantles. Reactions between ions and neutral molecules in ices may provide an alternative cold channel to complexity, as ion-neutral reactions are thought to have low or even no-energy barriers. Here we present a study of the kinetics and mechanisms of a potential ion-generating, acid-base reaction between NH 3 and HCOOH to form the salt NH + 4 HCOO −. We observe salt growth at temperatures as low as 15 K, indicating that this reaction is feasible in cold environments. The kinetics of salt growth are best fit by a two-step model involving a slow "pre-reaction" step followed by a fast reaction step. The reaction energy barrier is determined to be 70±30 K with a pre-exponential factor 1.4±0.4×10 −3 s −1. The pre-reaction rate varies under different experimental conditions and likely represents a combination of diffusion and orientation of reactant molecules. For a diffusion-limited case, the pre-reaction barrier is 770±110 K with a pre-exponential factor of ∼7.6×10 −3 s −1. Acid-base chemistry of common ice constituents is thus a potential cold pathway to generating ions in interstellar ices.
The Formation of Acetic Acid (CH3COOH) in Interstellar Ice Analogs
Astrophysical Journal, 2007
Binary ice mixtures of methane (CH 4 ) and carbon dioxide (CO 2 ) ices were irradiated at 12 K with energetic electrons to mimic the energy transfer processes that occur in the track of the trajectories of MeV cosmic-ray particles. The formation of trans-acetic acid (CH 3 COOH) was established through the appearance of new bands in the infrared spectrum at 1780, 1195, 1160, 1051, and 957 cm À1 ; two dimeric forms of acetic acid were assigned via absorptions at 1757 and 1723 cm À1 . During warm-up of the ice sample, the mass spectrometer recorded peaks of m/z values of 60 and 45 associated with the C 2 H 4 O 2 + and COOH + molecular ion and fragment, respectively. The kinetic fits of the column densities of the acetic acid molecule suggest that the initial step of the formation process appears to be the cleavage of a carbon-hydrogen bond from methane to generate the methyl radical plus atomic hydrogen. The hydrogen atom holds excess kinetic energy allowing it to overcome entrance barriers required to add to a carbon dioxide molecule, generating the carboxyl radical (HOCO). This radical can recombine with the methyl radical to form acetic acid molecule. Similar processes are expected to form acetic acid in the interstellar medium, thus providing alternatives to gasphase processes for the generation of complex chemical species whose fractional abundances compared to molecular hydrogen of typically a few ; 10 À9 cannot be accounted for by solely gas-phase chemistry.
Monthly Notices of the Royal Astronomical Society, 2017
The radiolysis of a 10:1 nitrogen:acetone mixture, condensed at 11 K, by 40 MeV 58 Ni 11+ ions is studied. These results are representative of studies concerning solar system objects exposed to cosmic rays. In the Kuiper Belt, region of Trans-Neptunian Objects (TNOs), acetone, N2 and other small molecules were detected and may be present on icy surfaces. Bombardment by cosmic rays triggers chemical reactions leading to synthesis of larger molecules. In this work, destruction cross sections of acetone and nitrogen molecules in solid phase are determined from a sequence of infrared spectra obtained at increasing ion beam fluence. The results are analyzed and compared with those of previous experiments performed with pure acetone. It is observed that the N2 column density decreases very fast, suggesting that nitrogen quickly leaves a porous sample under irradiation. The behavior of acetone in the mixture confirms that the ice formed by deposition of the vapor mixture is more porous than that of pure acetone ice. The most abundant molecular species formed from the mixture during irradiation are: C3H6, C2H6, N3, CO, CH4 and CO2. Some N-bearing species are also formed, but with low production yield. Comparing with pure acetone results, it is seen that dissolving acetone in nitrogen a ffects the formation cross sections of the new species: CH4, CO2 and H2CO, for example, have formation cross section smaller than the respective values for irradiated pure acetone, while those for CO and C2H6 species are higher. This fact can explain the presence of C2H6 even in regions on Pluto where CH4 is not pure, but diluted in a N2 matrix together with less abundant species. These results also show the formation of more complex molecules, such as HNCO, acetic acid and, possibility, glycine. The production of these complex molecules suggests the formation of small prebiotic species in objects beyond Neptune from acetone diluted in a N 2 matrix irradiated by cosmic rays. Formation cross sections for the new formed species are determined.
The Astrophysical Journal, 2009
Aminomethanol (NH 2 CH 2 OH) is formed at low temperature from the purely thermal reaction of NH 3 and H 2 CO in laboratory interstellar ice analogs. We report for the first time its infrared and mass spectra. We study its reaction and desorption kinetics using Fourier transform infrared spectroscopy and mass spectrometry. Its reaction rate is estimated to be k(T) = 0.05 × exp(−4.5(kJ mol −1)/RT) and its desorption energy to be E des = 58 ± 2 kJ mol −1. NH 2 CH 2 OH can also contribute to the 5-8 μm region of thermally processed ices encountered in many young stellar objects. Gas phase NH 2 CH 2 OH may be present in hot core regions, when the frozen material is desorbed.
Astrophysical Journal, 2005
The synthetic routes to form acetaldehyde [CH 3 CHO(X 1 A 0 )] in extraterrestrial ices were investigated experimentally in a contamination-free ultrahigh vacuum scattering machine. Binary ice mixtures of carbon monoxide [CO(X 1 AE + )] and methane [CH 4 (X 1 A 1 )] were condensed at 10 K onto a silver monocrystal and irradiated with 5 keV electrons to mimic the electronic energy transfer processes initiated by MeV cosmic-ray particle-induced -electrons in the ''ultratrack'' of MeV ion trajectories; the carbon monoxide-methane ices served as model compounds to simulate neighboring COÀCH 4 molecules in astrophysical ices, as present in cold molecular clouds and in cometary matter. Upon completion of the high-energy processing, the ice samples sublimed during the heating phase to 293 K, thus releasing the remaining reactants as well as the newly formed molecules into the gas phase. The experiment was monitored on line and in situ via a Fourier transform infrared (FTIR) spectrometer in absorption-reflection-absorption mode (solid state) and a quadrupole mass spectrometer (gas phase). Our investigations were combined with electronic structure calculations. At 10 K, the primary reaction step involved the cleavage of the carbon-hydrogen bond of the methane molecule via an electronic energy transfer process from the impinging electron to the methane molecule to form a methyl radical [CH 3 (X 2 A 00
Chiral molecule formation in interstellar ice analogs: alpha-aminoethanol NH 2 CH(CH 3 )OH
Astronomy & Astrophysics, 2010
Aims. Aminoalcohol molecules such as alpha-aminoethanol NH 2 CH(CH 3)OH may be aminoacid precursors. We attempt to characterize and detect this kind of molecules which is important to establish a possible link between interstellar molecules and life as we know it on Earth. Methods. We use Fourier transform infrared (FTIR) spectroscopy and mass spectrometry to study the formation of alphaaminoethanol NH 2 CH(CH 3)OH in H 2 O:NH 3 : CH 3 CHO ice mixtures. Isotopic substitution with 15 NH 3 and ab-initio calculation are used to confirm the identification of alpha-aminoethanol. Results. After investigating the thermal reaction of solid NH 3 and acetaldehyde CH 3 CHO at low temperature, we find that this reaction leads to the formation of a chiral molecule, the alpha aminoethanol NH 2 CH(CH 3)OH. For the first time, we report the infrared and mass spectra of this molecule. We also report on its photochemical behavior under VUV irradiation. We find that the main photoproduct is acetamide (NH 2 COCH 3). Data provided in this work indicates that alpha-aminoethanol is formed in one hour at 120 K and suggests that its formation in warm interstellar environments such as protostellar envelopes or cometary environments is likely.
Thermal chemistry of ice mixtures of astrophysical relevance
Advances in Space Research, 1997
Two different types of cryogenic thermal reactions have been indicated in astrophysical ice analogs. First, a very low activation barrier allows reactions between acids and bases and the formation of ions. Second, in the presence of traces of NHJ, formaldehyde polymerizes at temperatures in excess of N 60 K. The possible relevance of cryogenic thermal reactions in forming cometary matter is discussed.
Astronomy & Astrophysics, 2013
Context. Laboratory simulations on interstellar or cometary ice analogues are crucial to understand the formation of complex organic molecules that are detected in the interstellar medium (ISM). Results from this work give hints on physical and chemical processes occurring in space and can serve as a benchmark for dedicated space missions. Aims. The aim of this work is to consolidate the knowledge of ice evolution during the star formation process by investigating the influence of thermal reactions as a source of molecular complexity in the ISM. In this study, we are interested in the thermal reactivity between two interstellar molecules, formaldehyde (H 2 CO) and methylamine (CH 3 NH 2) in water ice analogues. Methods. We used Fourier transform infrared spectroscopy, mass spectrometry, and B3LYP calculations to investigate the thermal reaction between formaldehyde and methylamine (14 N and 15 N) at low temperature in water ice analogues. Results. We demonstrate that methylamine and formaldehyde quickly react in water ice analogues for astronomically relevant temperatures and form N-methylaminomethanol CH 3 NHCH 2 OH. The measured activation energy of this reaction, 1.1 ± 0.05 kJ mol −1 (1.8 ± 0.08 kJ mol −1 with methylamine 15 N), allows the reaction to proceed in interstellar ices, when the ices are gently warmed, as it occurs in young stellar objects, in photo-dissociation regions, or in comets. Therefore, CH 3 NHCH 2 OH is likely to be found in these objects. This hypothesis is confirmed by numerical simulations that clearly show that the formation of N-methylaminomethanol is likely at low temperature. Isotopic experiments as well as photochemical studies have also been performed to better characterise the ice evolution induced by heat and ultraviolet radiation during star formation. Key words. astrochemistry-molecular processes-methods: laboratory-ISM: molecules Gardner & McNesby (1982) and Ogura et al. (1989) proposed its formation from the UV photolysis of a gaseous mixture containing CH 4 and NH 3. Finally, Herbst (1985) proposed a gas phase methylamine formation from the methylium cation CH + 3 and NH 3. However, solid methylamine has never been detected in ice, so far. This could be due to its low abundance, but also to the difficulty to assign this compound from ices in infrared astronomical spectra. Works on ice analogues containing methylamine suggest that a plausible cause of its nonobservation in interstellar ices is its high reactivity at low temperature (Bossa et al. 2009a). Indeed, from a chemical point of view, CH 3 NH 2 is a better nucleophile and base than ammonia. This molecule can quickly react at low temperature in interstellar ice analogues with acids, such as HNCO, HCN, and HCOOH. In addition, methylamine reacts at low temperature with CO 2 , leading to the formation of methylammonium methylcarbamate (CH 3 NH + 3 CH 3 NHCOO −), which can be isomerised into glycine under UV irradiation (Bossa et al. 2009a). The measured activation barrier for this latter reaction, 3.7 kJ mol −1 , is compatible with low temperature observed in molecular clouds Article published by EDP Sciences
The Astrophysical Journal, 2015
Interstellar ices are submitted to energetic processes (thermal, UV, and cosmic-ray radiations) producing complex organic molecules. Laboratory experiments aim to reproduce the evolution of interstellar ices to better understand the chemical changes leading to the reaction, formation, and desorption of molecules. In this context, the thermal evolution of an interstellar ice analogue composed of water, carbon dioxide, ammonia, and formaldehyde is investigated. The ice evolution during the warming has been monitored by IR spectroscopy. The formation of hexamethylenetetramine (HMT) and polymethylenimine (PMI) are observed in the organic refractory residue left after ice sublimation. A better understanding of this result is realized with the study of another ice mixture containing methylenimine (a precursor of HMT) with carbon dioxide and ammonia. It appears that carbamic acid, a reaction product of carbon dioxide and ammonia, plays the role of catalyst, allowing the reactions toward HMT and PMI formation. This is the first time that such complex organic molecules (HMT, PMI) are produced from the warming (without VUV photolysis or irradiation with energetic particles) of abundant molecules observed in interstellar ices (H 2 O, NH 3 , CO 2 , H 2 CO). This result strengthens the importance of thermal reactions in the ices' evolution. HMT and PMI, likely components of interstellar ices, should be searched for in the pristine objects of our solar system, such as comets and carbonaceous chondrites.