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Summary of the energetics of the sim- ulated reactions and their products.

Summary of the energetics of the sim- ulated reactions and their products.

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Ethanol (CH3CH2OH) is a relatively common molecule, often found in star-forming regions. Recent studies suggest that it could be a parent molecule of several so-called interstellar complex organic molecules (iCOMs). However, the formation route of this species remains under debate. In the present work, we study the formation of ethanol through the...

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... it is a C-centered radical and contains both donor and acceptor H-bond atoms (the H and the C-end atoms, respectively), it tends to form H-bonded and hemibonded complexes with water ice molecules. The most relevant computed energetics of CCH reactivity on our ASW ice models are summarized in Table 3. On W18, R3 presents an activation barrier of 14.4 kJ mol −1 and, accordingly, it is not a priori an efficient path to form vinyl alcohol, although it could still be relevant if quantum tunnelling effects work. ...
Context 2
... hydrogenation of vinyl alcohol on grains leads to the formation of ethanol, as occurring in methanol formation from CO 115-119 and ethane formation from C 2 H 2 and C 2 H 4 . [120][121][122] The H-addition to vinyl alcohol is the only hydrogenation step not involving a barrierless radical-radical coupling and presents an energy barrier of 7.4 and 17.3 kJ mol −1 for the H1 and H2 channel (see Table 3). Thus, H1 is the most energetically favoured pathway for the formation of the ethanol radical precursor. ...

Citations

... Reliable ionization cross sections are required in plasma simulations of the combustion of ethanol in alternative fuel engines [52]. Ethanol is also found in interstellar environments and plays a significant part in the formation of organic compounds [53]. The BEB-SDCS for electronimpact ionization of ethanol are presented at various primary energies in Figure 8a,b. ...
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In the present work, we assess the effectiveness of singly differential cross sections (SDCS) due to electron-impact ionization by invoking the binary-encounter-Bethe (BEB) model on various atomic and molecular targets. The computed results were compared with the experimental and theoretical data. A good agreement was observed between the present and the available results. This agreement improves as the incident energy of the projectile increases. The model can be applied to compute the SDCS for the ions produced due to the electron-impact dissociative ionization process and the average energy due to the secondary electrons. Both these quantities are of interest in plasma processing and radiation physics.
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Acetaldehyde (CH3CHO) is ubiquitous in interstellar space and is important for astrochemistry as it can contribute to the formation of amino acids through reaction with nitrogen containing chemical species. Quantum chemical and reaction kinetics studies are reported for acetaldehyde formation from the chemical reaction of C(3P) with a methanol molecule adsorbed at the eighth position of a cubic water cluster. We present extensive quantum chemical calculations for total spin S = 1 and S = 0. The UωB97XD/6-311++G(2d,p) model chemistry is employed to optimize the structures, compute minimum energy paths and zero-point vibrational energies of all reaction steps. For the optimized structures, the calculated energies are refined by CCSD(T) single point computations. We identify four transition states on the triplet potential energy surface (PES), and one on the singlet PES. The reaction mechanism involves the intermediate formation of CH3OCH adsorbed on the ice cluster. The rate limiting step for forming acetaldehyde is the C–O bond breaking in CH3OCH to form adsorbed CH3 and HCO. We find two positions on the reaction path where spin crossing may be possible such that acetaldehyde can form in its singlet spin state. Using variational transition-state theory with multidimensional tunnelling we provide thermal rate constants for the energetically rate limiting step for both spin states and discuss two routes to acetaldehyde formation. As expected, quantum effects are important at low temperatures.
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Glycine (Gly), NH2CH2COOH, is the simplest amino acid. Although it has not been directly detected in the interstellar gas-phase medium, it has been identified in comets and meteorites, and its synthesis in these environments has been simulated in terrestrial laboratory experiments. Likewise, condensation of Gly to form peptides in scenarios resembling those present in a primordial Earth has been demonstrated experimentally. Thus, Gly is a paradigmatic system for biomolecular building blocks to investigate how they can be synthesized in astrophysical environments, transported and delivered by fragments of asteroids (meteorites, once they land on Earth) and comets (interplanetary dust particles that land on Earth) to the primitive Earth, and there react to form biopolymers as a step towards the emergence of life. Quantum chemical investigations addressing these Gly-related events have been performed, providing fundamental atomic-scale information and quantitative energetic data. However, they are spread in the literature and difficult to harmonize in a consistent way due to different computational chemistry methodologies and model systems. This review aims to collect the work done so far to characterize, at a quantum mechanical level, the chemical life of Gly, i.e., from its synthesis in the interstellar medium up to its polymerization on Earth.