Kinetics and Mechanisms of the Acid-Base Reaction Between NH3AND Hcooh in Interstellar Ice Analogs (original) (raw)
Related papers
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, 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.
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.
arXiv (Cornell University), 2022
In the coldest (10-20 K) regions of the interstellar medium, the icy surfaces of interstellar grains serve as solid-state supports for chemical reactions. Among their plausible roles, that of third body is advocated, in which the reaction energies of surface reactions dissipate throughout the grain, stabilizing the product. This energy dissipation process is poorly understood at the atomic scale, although it can have a high impact on Astrochemistry. Here, we study, by means of quantum mechanical simulations, the formation of NH3 via successive H-additions to atomic N on water ice surfaces, paying special attention to the third body role. We first characterize the hydrogenation reactions and the possible competitive processes (i.e., H-abstractions), in which the H-additions are more favourable than the H-abstractions. Subsequently, we study the fate of the hydrogenation reaction energies by means of ab initio molecular dynamics simulations. Results show that around 58-90% of the released energy is quickly absorbed by the ice surface, inducing a temporary increase of the ice temperature. Different energy dissipation mechanisms are distinguished. One mechanism, more general, is based on the coupling of the highly excited vibrational modes of the newly formed species and the libration modes of the icy water molecules. A second mechanism, exclusive during the NH 3 formation, is based on the formation of a transient H 3 O + /NH − 2 ion pair, which significantly accelerates the energy transfer to the surface. Finally, the astrophysical implications of our findings relative to the interstellar synthesis of NH 3 and its chemical desorption into the gas are discussed.
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
Formation of complex organic molecules in ice mantles: An ab initio molecular dynamics study
Astronomy & Astrophysics
We present a detailed simulation of a dust grain covered by a decamer of (CH3OH)10-ice-mantle, bombarded by an OH− closed-shell molecule with kinetic energies from 10–22 eV. The chemical pathways are studied through Born-Oppenheimer (ab initio) molecular dynamics. The simulations show that methanol ice-mantles can be a key generator of complex organic molecules (COMs). We report the formation of COMs such as methylene glycol (CH2(OH)2) and the OCH2OH radical, which have not been detected yet in the interstellar medium (ISM). We discuss the chemical formation of new species through the reaction of CH3OH with the hydroxyl projectile. The dependence of the outcome on the kinetic energy of the projectile and the implications for the observation and detection of these molecules might explain why the methoxy radical (CH3 ⋅ ) has been observed in a wider range of astrophysical environments than the hydroxymethyl (CH2OH ⋅) isomer. Because of the projectile kinetic energies required for the...
Astrophysical Journal, 2010
We present direct evidence for ammonium ion (NH4+) formation through ultraviolet (UV) photolysis of NH3-H2O mixture ice that does not contain acids. NH4+ forms by the reaction of NH3 with protonic defects (H3O+) in the UV-photolyzed ice. Our observations may explain the deficient counter-anions in interstellar ice relative to the abundance of NH4+. Also, H3O+ may play an important role in the acid-base chemistry of interstellar ice in UV-irradiating environments. IR absorption results suggest that NH4+ is a potential contributor to the interstellar 6.85 μm band but is not a dominant component.
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.
Formation of NH2CHO and CH3CHO upon UV Photoprocessing of Interstellar Ice Analogs
The Astrophysical Journal, 2020
Complex organic molecules (COMs) can be produced by energetic processing of interstellar ice mantles accreted on top of dust grains. Two COMs with proposed energetic ice formation pathways are formamide and acetaldehyde. Both have been detected in Solar System comets, and in different circumstellar and interstellar environments. In this work, we study the NH 2 CHO and CH 3 CHO formation upon UV photoprocessing of CO:NH 3 and CO:CH 4 ice samples. The conversion from NH. 2 radicals to NH 2 CHO is 2−16 times higher than the conversion from CH. 3 radicals to CH 3 CHO under the explored experimental conditions, likely because the formation of the latter competes with the formation of larger hydrocarbons. In addition, the conversion of NH. 2 into NH 2 CHO at 10 K increases with the NH 3 abundance in the ice, and also with the temperature in CO-dominated CO:NH 3 ices. This is consistent with the presence of a small NH. 2 and HCO. reorientation barrier for the formation of NH 2 CHO, which is overcome with an increase in the ice temperature. The measured NH 2 CHO and CH 3 CHO formation efficiencies and rates are similar to those found during electron irradiation of the same ice samples under comparable conditions, suggesting that both UV photons and cosmic rays would have similar contributions to the solid-state formation of these species in space. Finally, the measured conversion yields (up to one order of magnitude higher for NH 2 CHO) suggest that in circumstellar environments, where the observed NH 2 CHO/CH 3 CHO abundance ratio is ∼0.1, there are likely additional ice and/or gas phase formation pathways for CH 3 CHO.
ACS earth and space chemistry, 2019
The interstellar medium (ISM) is rich in molecules, from simple diatomic to complex organic ones, some of which have a biotic potential. A notable example, in this respect, is represented by the socalled interstellar complex organic molecules (iCOMs). Interestingly, the various phases involved in the formation of Solar-type planetary systems lead to an increasing chemical complexity, in which, at each step, more complex molecules form. In dark molecular clouds, dust grains are covered by ice mantles, mainly made up of H 2 O but also of other volatiles species such as CO, NH 3 , CO 2 , CH 4 and CH 3 OH. Although their mass is one hundred times lower than the gas-phase matter, these ice-covered grains play a fundamental role in the interstellar chemical complexity as some important reactions are exclusively catalyzed by their surfaces. For example, one of the current paradigms on the iCOMs formation assumes that iCOMs are synthesized on the ice mantle surfaces, in which reactants accrete and diffuse to finally react. As the usual approaches employed in astrochemistry (i.e., spectroscopic astronomical observations, astrochemical modelling and laboratory experiments) cannot easily provide details on the iCOMs formation processes occurring