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Artykuły w czasopismach na temat "Interstellar Medium - Radical‐Molecule Reactions"
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Brigiano, Flavio Siro, Yannick Jeanvoine, Antonio Largo i Riccardo Spezia. "The formation of urea in space". Astronomy & Astrophysics 610 (luty 2018): A26. http://dx.doi.org/10.1051/0004-6361/201731610.
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Context. Many organic molecules have been observed in the interstellar medium thanks to advances in radioastronomy, and very recently the presence of urea was also suggested. While those molecules were observed, it is not clear what the mechanisms responsible to their formation are. In fact, if gas-phase reactions are responsible, they should occur through barrierless mechanisms (or with very low barriers). In the past, mechanisms for the formation of different organic molecules were studied, providing only in a few cases energetic conditions favorable to a synthesis at very low temperature. A particularly intriguing class of such molecules are those containing one N–C–O peptide bond, which could be a building block for the formation of biological molecules. Urea is a particular case because two nitrogen atoms are linked to the C–O moiety. Thus, motivated also by the recent tentative observation of urea, we have considered the synthetic pathways responsible to its formation. Aims. We have studied the possibility of forming urea in the gas phase via different kinds of bi-molecular reactions: ion-molecule, neutral, and radical. In particular we have focused on the activation energy of these reactions in order to find possible reactants that could be responsible for to barrierless (or very low energy) pathways. Methods. We have used very accurate, highly correlated quantum chemistry calculations to locate and characterize the reaction pathways in terms of minima and transition states connecting reactants to products. Results. Most of the reactions considered have an activation energy that is too high; but the ion-molecule reaction between NH2OHNH2OH2+ and formamide is not too high. These reactants could be responsible not only for the formation of urea but also of isocyanic acid, which is an organic molecule also observed in the interstellar medium.
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West, Niclas A., Edward Rutter, Mark A. Blitz, Leen Decin i Dwayne E. Heard. "Low temperature gas phase reaction rate coefficient measurements: Toward modeling of stellar winds and the interstellar medium". Proceedings of the International Astronomical Union 15, S350 (kwiecień 2019): 382–83. http://dx.doi.org/10.1017/s1743921319007531.
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AbstractStellar winds of Asymptotic Giant Branch (AGB) stars are responsible for the production of ∼85% of the gas molecules in the interstellar medium (ISM), and yet very few of the gas phase rate coefficients under the relevant conditions (10 – 3000 K) needed to model the rate of production and loss of these molecules in stellar winds have been experimentally measured. If measured at all, the value of the rate coefficient has often only been obtained at room temperature, with extrapolation to lower and higher temperatures using the Arrhenius equation. However, non-Arrhenius behavior has been observed often in the few measured rate coefficients at low temperatures. In previous reactions studied, theoretical simulations of the formation of long-lived pre-reaction complexes and quantum mechanical tunneling through the barrier to reaction have been utilized to fit these non-Arrhenius behaviours of rate coefficients.Reaction rate coefficients that were predicted to produce the largest change in the production/loss of Complex Organic Molecules (COMs) in stellar winds at low temperatures were selected from a sensitivity analysis. Here we present measurements of rate coefficients using a pulsed Laval nozzle apparatus with the Pump Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique. Gas flow temperatures between 30 – 134 K have been produced by the University of Leeds apparatus through the controlled expansion of N2 or Ar gas through Laval nozzles of a range of Mach numbers between 2.49 and 4.25.Reactions of interest include those of OH, CN, and CH with volatile organic species, in particular formaldehyde, a molecule which has been detected in the ISM. Kinetics measurements of these reactions at low temperatures will be presented using the decay of the radical reagent. Since formaldehyde and the formal radical (HCO) are potential building blocks of COMs in the interstellar medium, low temperature reaction rate coefficients for their production and loss can help to predict the formation pathways of COMs observed in the interstellar medium.
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Parker, Dorian S. N., Ralf I. Kaiser, Oleg Kostko, Tyler P. Troy, Musahid Ahmed, Bing-Jian Sun, Shih-Hua Chen i A. H. H. Chang. "On the formation of pyridine in the interstellar medium". Physical Chemistry Chemical Physics 17, nr 47 (2015): 32000–32008. http://dx.doi.org/10.1039/c5cp02960k.
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The nitrogen bearing aromatic molecule pyridine (C5H5N) is revealed to form in high temperature environments simulating conditions in carbon-rich circumstellar envelopes via the reaction of the cyano vinyl radical with vinyl cyanide.
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Canosa, André. "Gas phase reaction kinetics of complex organic molecules at temperatures of the interstellar medium: The OH + CH3OH case". Proceedings of the International Astronomical Union 15, S350 (kwiecień 2019): 35–40. http://dx.doi.org/10.1017/s1743921319006446.
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AbstractRecent experimental and theoretical works concerning gas-phase radical-neutral reactions involving Complex Organic Molecules are reviewed in the context of cold interstellar objects with a special emphasis on the OH + CH3OH reaction and its potential impact on the formation of CH3O.
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Miksch, April M., Annalena Riffelt, Ricardo Oliveira, Johannes Kästner i Germán Molpeceres. "Hydrogenation of small aromatic heterocycles at low temperatures". Monthly Notices of the Royal Astronomical Society 505, nr 3 (27.05.2021): 3157–64. http://dx.doi.org/10.1093/mnras/stab1514.
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ABSTRACT The recent wave of detections of interstellar aromatic molecules has sparked interest in the chemical behaviour of aromatic molecules under astrophysical conditions. In most cases, these detections have been made through chemically related molecules, called proxies, that implicitly indicate the presence of a parent molecule. In this study, we present the results of the theoretical evaluation of the hydrogenation reactions of different aromatic molecules (benzene, pyridine, pyrrole, furan, thiophene, silabenzene, and phosphorine). The viability of these reactions allows us to evaluate the resilience of these molecules to the most important reducing agent in the interstellar medium, the hydrogen atom (H). All significant reactions are exothermic and most of them present activation barriers, which are, in several cases, overcome by quantum tunnelling. Instanton reaction rate constants are provided between 50 and 500 K. For the most efficiently formed radicals, a second hydrogenation step has been studied. We propose that hydrogenated derivatives of furan and pyrrole, especially 2,3-dihydropyrrole, 2,5-dihydropyrrole, 2,3-dihydrofuran, and 2,5-dihydrofuran, are promising candidates for future interstellar detections.
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Doddipatla, Srinivas, Galiya R. Galimova, Hongji Wei, Aaron M. Thomas, Chao He, Zhenghai Yang, Alexander N. Morozov, Christopher N. Shingledecker, Alexander M. Mebel i Ralf I. Kaiser. "Low-temperature gas-phase formation of indene in the interstellar medium". Science Advances 7, nr 1 (styczeń 2021): eabd4044. http://dx.doi.org/10.1126/sciadv.abd4044.
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Polycyclic aromatic hydrocarbons (PAHs) are fundamental molecular building blocks of fullerenes and carbonaceous nanostructures in the interstellar medium and in combustion systems. However, an understanding of the formation of aromatic molecules carrying five-membered rings—the essential building block of nonplanar PAHs—is still in its infancy. Exploiting crossed molecular beam experiments augmented by electronic structure calculations and astrochemical modeling, we reveal an unusual pathway leading to the formation of indene (C9H8)—the prototype aromatic molecule with a five-membered ring—via a barrierless bimolecular reaction involving the simplest organic radical—methylidyne (CH)—and styrene (C6H5C2H3) through the hitherto elusive methylidyne addition–cyclization–aromatization (MACA) mechanism. Through extensive structural reorganization of the carbon backbone, the incorporation of a five-membered ring may eventually lead to three-dimensional PAHs such as corannulene (C20H10) along with fullerenes (C60, C70), thus offering a new concept on the low-temperature chemistry of carbon in our galaxy.
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Zaverkin, V., T. Lamberts, M. N. Markmeyer i J. Kästner. "Tunnelling dominates the reactions of hydrogen atoms with unsaturated alcohols and aldehydes in the dense medium". Astronomy & Astrophysics 617 (wrzesień 2018): A25. http://dx.doi.org/10.1051/0004-6361/201833346.
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Hydrogen addition and abstraction reactions play an important role as surface reactions in the buildup of complex organic molecules in the dense interstellar medium. Addition reactions allow unsaturated bonds to be fully hydrogenated, while abstraction reactions recreate radicals that may undergo radical–radical recombination reactions. Previous experimental work has indicated that double and triple C–C bonds are easily hydrogenated, but aldehyde –C=O bonds are not. Here, we investigate a total of 29 reactions of the hydrogen atom with propynal, propargyl alcohol, propenal, allyl alcohol, and propanal by means of quantum chemical methods to quantify the reaction rate constants involved. First of all, our results are in good agreement with and can explain the observed experimental findings. The hydrogen addition to the aldehyde group, either on the C or O side, is indeed slow for all molecules considered. Abstraction of the H atom from the aldehyde group, on the other hand, is among the faster reactions. Furthermore, hydrogen addition to C–C double bonds is generally faster than to triple bonds. In both cases, addition on the terminal carbon atom that is not connected to other functional groups is easiest. Finally, we wish to stress that it is not possible to predict rate constants based solely on the type of reaction: the specific functional groups attached to a backbone play a crucial role and can lead to a spread of several orders of magnitude in the rate constant.
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Ferrero, Stefano, Cecilia Ceccarelli, Piero Ugliengo, Mariona Sodupe i Albert Rimola. "Formation of Complex Organic Molecules on Interstellar CO Ices? Insights from Computational Chemistry Simulations". Astrophysical Journal 951, nr 2 (1.07.2023): 150. http://dx.doi.org/10.3847/1538-4357/acd192.
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Abstract The carbon (3P) atom is a reactive species that, according to laboratory experiments and theoretical calculations, condensates with interstellar ice components. This fact is of uttermost importance for the chemistry in the interstellar medium (ISM) because the condensation reaction is barrierless, and the subsequent species formed are still reactive given their open-shell character. Carbon condensation on CO-rich ices forms the C=C=O (3Σ−) species, which can be easily hydrogenated twice to form ketene (H2CCO). Ketene is very reactive in terrestrial conditions, usually found as an intermediate that is difficult to isolate in chemical synthesis laboratories. These characteristics suggest that ketene can be a good candidate to form interstellar complex organic molecules via a two-step process, i.e., its activation followed by a radical–radical coupling. In this work, reactions between ketene and atomic H and the OH and NH2 radicals on a CO-rich ice model have been explored by means of quantum chemical calculations complemented by kinetic calculations to evaluate if they are favorable in the ISM. Results indicate that the addition of H to ketene (helped by tunneling) to form the acetyl radical (CH3CO) is the most preferred path as the reactions with OH and NH2 possess activation energies (≥9 kJ mol−1) hard to surmount in the ISM conditions unless external processes provide energy to the system. Thus, acetaldehyde (CH3CHO) and, probably, ethanol (CH3CH2OH) formation via further hydrogenations, are the possible unique operating synthetic routes. Moreover, from the computed, relatively large binding energies of OH and NH2 on CO ice, slow diffusion is expected, hampering possible radical–radical couplings with CH3CO. The astrophysical implications of these findings are discussed considering the incoming James Webb Space Telescope observations.
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Lu, Shiru, Zhisen Meng, Peng Xie, Enwei Liang i Zhao Wang. "Gas-phase formation of interstellar nucleobases from dehydrogenated formamide and vinyl cyanide". Astronomy & Astrophysics 656 (grudzień 2021): A84. http://dx.doi.org/10.1051/0004-6361/202140744.
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Context. Cytosine, thymine, and uracil are three of the five primary nucleobases that function as the fundamental units of the genetic code in nucleic acids. In searching the extraterrestrial origins of microscopic life, previous studies have reported formation routes of nucleobases in interstellar ice analogs. The present work explores the possibility that nucleobases could form from small molecules through gas-phase reactions in the interstellar medium (ISM). Aims. We aim to search energetically favorable synthetic routes toward the formation of cytosine, thymine, and uracil via gas-phase reactions, using first principles calculations. Based on the computation of a reaction energy barrier and reactant formation energy, we tried to identify the specific interstellar environments favorable to the formation of the nucleobases, with respect to the previously reported detection of relevant reactants in the ISM. Methods. Density functional theory calculations were carried out to investigate the chemical reaction pathways using the M06 functional with 6-31+G(d,p)/6-311++G(d,p) basis sets. An ab initio Møller-Plesset perturbation theory in the second order (MP2) was also used to corroborate the results. Results. We report synthetic routes toward the formation of cytosine, thymine, and uracil through gas-phase reactions between partially dehydrogenated formamide (H2NCHO) and vinyl cyanide (H2CCHCN). The most energetically favorable pathway to the formation of 1H-pyrimidin-2-one (C4H4N2O), a direct precursor of nucleobases, was found in a molecule-radical reaction between HNCHO and H2CCHCN, with an energy barrier of 19.3 kcal mol−1. The energy barriers for the optimal reaction pathways between C4H4N2O and amino, methyl, or hydroxyl to finally produce cytosine, thymine, or uracil are about 11.3, 18.6, or 19.9 kcal mol−1, respectively. Conclusions. The optimal energy barriers of 19.3 and 23.8 kcal mol−1 roughly correspond to a reaction rate coefficient of 10−11 cm3 s−1 at 180 and 220 K, respectively. This indicates that the reaction could be thermally feasible through a gas-phase reaction in hot molecular cores or in the inner part of the protoplanetary disks. In contrast, the energy barriers for the reactions between other dehydrogenated radicals and molecules are relatively high, which corresponds to the extinction energy of far-ultraviolet photons in photo-dissociation regions. Furthermore, the computed pathways suggest that prior H migration in the reactants could be the key rate-determining process for the synthesis of the primary nucleobases.
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Inostroza, Natalia, Diego Mardones, Jose Cernicharo, Hans Zinnecker, Jixing Ge, Nelson Aria, Patricio Fuentealba i Carlos Cardenas. "Formation of complex organic molecules in ice mantles: An ab initio molecular dynamics study". Astronomy & Astrophysics 629 (30.08.2019): A28. http://dx.doi.org/10.1051/0004-6361/201834035.
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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 these reactions to occur, we suggest that these processes are likely relevant in the production of COMs in photodissociation and shock regions produced by high-velocity jets and outflows from young stellar objects.
Rozprawy doktorskie na temat "Interstellar Medium - Radical‐Molecule Reactions"
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Barthel, Robert. "Growth of unsaturated, cyclic, and polycyclic aromatic hydrocarbons: Reactions under the conditions of the interstellar medium". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1238024025498-21465.
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Hydrocarbons, in particular polycyclic aromatic hydrocarbons (PAHs), have been long discussed to be carriers of interstellar infrared (IR) emission and ultraviolet (UV) absorption features. Yet, their origin in dense phases of the interstellar medium (ISM), such as molecular clouds, remains unclear. In this work, growth mechanisms based on ion-molecule reactions between cationic PAHs/hydrocarbons and methyne (CH) were investigated. The reaction type and the precursor were derived and selected from known chemical and physical properties of the ISM. These chemical reactions were characterised by calculating branching ratios (based on cross sections) and capture rate coefficients, minimum reaction paths, reaction enthalpies, thermal equilibrium constants, and microcanonic isomerisation and radiative deactivation rate coefficients. In order to cope with the variety of reaction parameters, a hierarchic workflow scheme was set up. First, the reaction potential energy surface was sampled by molecular dynamics simulations. Then, minimum energy paths of the most probable reaction channels were investigated. Finally, molecular and kinetic properties of stationary points were calculated. The quantum chemical level of theory was increased at each step from DFTB (tight-binding density-functional), to DFT, and finally to post-Hartree-Fock methods. Results on CH based hydrocarbon growth showed the transition from non-cyclic hydrocarbons to cyclic and aromatic structures and from cyclic to polycyclic aromatic hydrocarbons. Additionally, the reactive collisions between hydrocarbons and CH were found to produce sufficient energy for isomerisation and fragmentation processes even at ultra low temperatures. In all, the results indicate that methyne might be a proper precursor for the formation of large interstellar PAHsKohlenwasserstoffe, insbesondere polyzyklische Kohlenwasserstoffe (engl. PAHs), werden seit einigen Jahren als Mitverursacher interstellar IR-Emissions- und UV-Absorptionsbanden angesehen und diskutiert. Dabei ist die Herkunft dieser Moleküle in den dichten Phasen des interstellaren Mediums (ISM) aber noch nicht aufgeklärt. In dieser Arbeit wurden daher die Bildungsmechanismen, welche auf Ion-Molekül-Reaktionen zwischen kationischen PAHs und Kohlenwasserstoffen und dem Molekül CH beruhen, untersucht. Sowohl der Reaktionstyp als auch der Präkursor wurden anhand von bekannten physikalischen und chemischen Eigenschaften des ISM abgeleitet und ausgewählt. Die Analyse der chemischen Reaktionen basierte auf Berechnungen zur Produktzusammensetzung und Einfangsratenkoeffizienten (welche wiederum aus berechneten Reaktionsquerschnitten hervorgingen) Minimumenergiepfade (MEP), Reaktionsenthalpien, thermische Gleichgewichtskonstanten und mikrokanonische Isomerisierungs- und Strahlungsdeaktivierungs-Ratenkoeffizienten. Um der Vielzahl an Reaktionsparameter gerecht zu werden, wurden die Berechnungsmethoden entsprechend eines hierarischen Fließschemas kombiniert. Hierzu wurden zuerst durch Molekulardynamik-Simulationen die Reaktionspotentialenergieflächen abgerastert. Auf der nächsten Stufe wurden statistisch bedeutsame Reaktionskanäle bezüglich ihrer Minimumenergiepfade untersucht. Den Abschluss bildete die Berechnung molekularer und kinetischer Charakteristika stationärer Punkte auf einem MEP. Entsprechend dieses Schemas wurde die quantenchemische Genauigkeit auf jeder Stufe von approximativer DFT über DFT zu post-Hartree-Fock verändert. Die Ergebnisse des CH-basierten Kohlenwasserstoffwachstums zeigten einen Übergang von nichtzyklischen zu zyklischen and aromatischen Strukturen, sowie von zyklischen zu polyzyklischen Kohlenwasserstoffen. Außerdem zeigte sich, dass reaktive Kollisionen zwischen Kohlenwasserstoffen und CH auch bei Tiefsttemperaturen immer ausreichend Energie für Isomerisierungs- und Fragmentationsprozesse liefert. Die Ergebnisse dieser Arbeit lassen den Schluss zu, dass CH ein geeigneter Präkursor für die Bildung großer interstellarer PAH ist
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Barthel, Robert. "Growth of unsaturated, cyclic, and polycyclic aromatic hydrocarbons: Reactions under the conditions of the interstellar medium". Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23589.
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Hydrocarbons, in particular polycyclic aromatic hydrocarbons (PAHs), have been long discussed to be carriers of interstellar infrared (IR) emission and ultraviolet (UV) absorption features. Yet, their origin in dense phases of the interstellar medium (ISM), such as molecular clouds, remains unclear. In this work, growth mechanisms based on ion-molecule reactions between cationic PAHs/hydrocarbons and methyne (CH) were investigated. The reaction type and the precursor were derived and selected from known chemical and physical properties of the ISM. These chemical reactions were characterised by calculating branching ratios (based on cross sections) and capture rate coefficients, minimum reaction paths, reaction enthalpies, thermal equilibrium constants, and microcanonic isomerisation and radiative deactivation rate coefficients. In order to cope with the variety of reaction parameters, a hierarchic workflow scheme was set up. First, the reaction potential energy surface was sampled by molecular dynamics simulations. Then, minimum energy paths of the most probable reaction channels were investigated. Finally, molecular and kinetic properties of stationary points were calculated. The quantum chemical level of theory was increased at each step from DFTB (tight-binding density-functional), to DFT, and finally to post-Hartree-Fock methods. Results on CH based hydrocarbon growth showed the transition from non-cyclic hydrocarbons to cyclic and aromatic structures and from cyclic to polycyclic aromatic hydrocarbons. Additionally, the reactive collisions between hydrocarbons and CH were found to produce sufficient energy for isomerisation and fragmentation processes even at ultra low temperatures. In all, the results indicate that methyne might be a proper precursor for the formation of large interstellar PAHs.Kohlenwasserstoffe, insbesondere polyzyklische Kohlenwasserstoffe (engl. PAHs), werden seit einigen Jahren als Mitverursacher interstellar IR-Emissions- und UV-Absorptionsbanden angesehen und diskutiert. Dabei ist die Herkunft dieser Moleküle in den dichten Phasen des interstellaren Mediums (ISM) aber noch nicht aufgeklärt. In dieser Arbeit wurden daher die Bildungsmechanismen, welche auf Ion-Molekül-Reaktionen zwischen kationischen PAHs und Kohlenwasserstoffen und dem Molekül CH beruhen, untersucht. Sowohl der Reaktionstyp als auch der Präkursor wurden anhand von bekannten physikalischen und chemischen Eigenschaften des ISM abgeleitet und ausgewählt. Die Analyse der chemischen Reaktionen basierte auf Berechnungen zur Produktzusammensetzung und Einfangsratenkoeffizienten (welche wiederum aus berechneten Reaktionsquerschnitten hervorgingen) Minimumenergiepfade (MEP), Reaktionsenthalpien, thermische Gleichgewichtskonstanten und mikrokanonische Isomerisierungs- und Strahlungsdeaktivierungs-Ratenkoeffizienten. Um der Vielzahl an Reaktionsparameter gerecht zu werden, wurden die Berechnungsmethoden entsprechend eines hierarischen Fließschemas kombiniert. Hierzu wurden zuerst durch Molekulardynamik-Simulationen die Reaktionspotentialenergieflächen abgerastert. Auf der nächsten Stufe wurden statistisch bedeutsame Reaktionskanäle bezüglich ihrer Minimumenergiepfade untersucht. Den Abschluss bildete die Berechnung molekularer und kinetischer Charakteristika stationärer Punkte auf einem MEP. Entsprechend dieses Schemas wurde die quantenchemische Genauigkeit auf jeder Stufe von approximativer DFT über DFT zu post-Hartree-Fock verändert. Die Ergebnisse des CH-basierten Kohlenwasserstoffwachstums zeigten einen Übergang von nichtzyklischen zu zyklischen and aromatischen Strukturen, sowie von zyklischen zu polyzyklischen Kohlenwasserstoffen. Außerdem zeigte sich, dass reaktive Kollisionen zwischen Kohlenwasserstoffen und CH auch bei Tiefsttemperaturen immer ausreichend Energie für Isomerisierungs- und Fragmentationsprozesse liefert. Die Ergebnisse dieser Arbeit lassen den Schluss zu, dass CH ein geeigneter Präkursor für die Bildung großer interstellarer PAH ist.
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Pearcy, Adam C. "Non-covalent and covalent interactions between phenylacetylene and quinoline radical cations with polar and non-polar molecules in the gas phase". VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5990.
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Gas phase molecular clusters present an ideal medium for observing factors that drive chemical reactions without outside interferences from excessive solvent molecules. Introducing an ion into the cluster promotes ion-molecule interactions that may manifest in a variety of non-covalent or even covalent binding motifs and are of significant importance in many fields including atmospheric and astronomical sciences. For instance, in outer space, molecules are subject to ionizing radiation where ion-molecule reactions become increasingly competitive to molecule-molecule interactions. To elucidate individual ion-molecule interaction information, mass spectrometry was used in conjunction with appropriate theoretical calculations.
Three main categories of experiment were conducted in this dissertation. The first of which were thermochemical equilibrium measurements where an ion was introduced to an ion mobility drift cell wherein thermalizing collisions occur with helium buffer gas facilitating a reversible reaction with a neutral molecule allowing the standard changes in enthalpy and entropy to be determined. The second type of experiment was an ion mobility experiment where an ionized homo- or hetero-cluster was injected into the drift cell at specific conditions allowing the reduced mobility and collisional cross-section to be evaluated. Thirdly, kinetics measurements were taken following injection of an ion into the drift cell were an irreversible reaction ensued with the neutral species hindering equilibrium, but prompting rate constant assessment.
Previous research has laid the groundwork for this dissertation as the results and discussion contained herein will build upon existing data while maintaining originality. For example, past work has given support for ion-molecule reactions involving precursor species such as acetylene and hydrogen cyanide to form more complex organics, perhaps leading to biologically relevant species. The chemical systems studied for this research are either ionized substituted benzenes like phenylacetylene and benzonitrile or polycyclic aromatic nitrogen-containing hydrocarbons like quinoline and quinoxaline interacting with a variety of neutral species.
Hydrogen bonding and its many sub-sections are of the utmost importance to the kinds of reactions studied here. Past work has shown the tendency of organic radical cations to form conventional and unconventional ionic hydrogen bonds with gas phase solvents. Other non-covalent modes of interaction have also been detected in addition to the formation of covalently bound species. Gas phase reactions studied here will explore, via mass-selected ion mobility, reversible and irreversible reactions leading to binding enthalpy and entropy and rate constant determination, respectively, in addition to collisional cross-section determination.
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Stavish, Leah. "Selected Ion Flow Tube studies of ion-molecule reactions relevant to the interstellar medium and Titan's atmosphere". 2009. http://purl.galileo.usg.edu/uga%5Fetd/stavish%5Fleah%5F200912%5Fms.
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Thesis (M.S.)--University of Georgia, 2009.Directed by Nigel G. Adams. Includes an article accepted by, and an article published in, International journal of mass spectrometry. Includes bibliographical references.
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Jackson, Douglas M. "Selected ion flow tube studies of interest to the chemistry of ion-molecule reactions in the interstellar medium". 2007. http://purl.galileo.usg.edu/uga%5Fetd/jackson%5Fdouglas%5Fm%5F200705%5Fms.
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Tran, Thuy Dung. "Formování vody reakcemi aniontů i kationtů s molekulárním vodíkem při nízkých teplotách". Doctoral thesis, 2020. http://www.nusl.cz/ntk/nusl-411460.
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In the present work, the results of the experimental study of reactions of ions with molecular hydrogen in the temperature range 15 - 300 K using a 22-pole ion trap apparatus are presented. The reaction of OD- with para-enriched hydrogen was studied using a combination of the 22-pole ion trap apparatus with a para-hydrogen generator. Also reactions of O- with H2, D2, and HD were studied. These reactions have a channel of water production and a channel of hydrogen or deuterium transfer. Another field of study was a sequence of reactions of oxygen hydride cations with H2 and D2 which leads to the production of H3O+ or its isotopic variant, specifically reactions OH+ with H2, H2O+ with H2, D2O+ with H2, and D2O+ with D2. This reaction chain can be followed by the electron recombination of H3O+ or its isotopologue, which has a channel of water production.
Części książek na temat "Interstellar Medium - Radical‐Molecule Reactions"
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Germain, Aurèle, Marta Corno i Piero Ugliengo. "Computing Binding Energies of Interstellar Molecules by Semiempirical Quantum Methods: Comparison Between DFT and GFN2 on Crystalline Ice". W Computational Science and Its Applications – ICCSA 2021, 632–45. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-86976-2_43.
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AbstractInterstellar Grains (IGs) spread in the Interstellar Medium (ISM) host a multitude of chemical reactions that could lead to the production of interstellar Complex Organic Molecules (iCOMs), relevant in the context of prebiotic chemistry. These IGs are composed of a silicate-based core covered by several layers of amorphous water ice, known as a grain mantle. Molecules from the ISM gas-phase can be adsorbed at the grain surfaces, diffuse and react to give iCOMs and ultimately desorbed back to the gas phase. Thus, the study of the Binding Energy (BE) of these molecules at the water ice grain surface is important to understand the molecular composition of the ISM and its evolution in time. In this paper, we propose to use a recently developed semiempirical quantum approach, named GFN-xTB, and more precisely the GFN2 method, to compute the BE of several molecular species at the crystalline water ice slab model. This method is very cheap in term of computing power and time and was already showed in a previous work to be very accurate with small water clusters. To support our proposition, we decided to use, as a benchmark, the recent work published by some of us in which a crystalline model of proton-ordered water ice (P-ice) was adopted to predict the BEs of 21 molecules relevant in the ISM. The relatively good results obtained confirm GFN2 as the method of choice to model adsorption processes occurring at the icy grains in the ISM. The only notable exception was for the CO molecule, in which both structure and BE are badly predicted by GFN2, a real pity due to the relevance of CO in astrochemistry.
Streszczenia konferencji na temat "Interstellar Medium - Radical‐Molecule Reactions"
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Frum, C. I., J. J. OH, E. A. Cohen i H. M. Pickett. "High Resolution Infrared Fourier Transform Emission Spectroscopy and Rotational Spectroscopy of Metal Hydrides: 2Σ+ State of CaH". W High Resolution Fourier Transform Spectroscopy. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/hrfts.1992.thd6.
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Calcium hydride is an important astrophysical molecule which has been detected in the Sun [1,2] and other stars [3]. It is also believed that this free radical is an important constituent of the interstellar medium [4]. However, a search for the CaH in interstellar medium is hindered by the unavailability of accurate frequencies for the low-N rotational transitions.
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Thaddeus, Patrick. "Carbenes in the Interstellar Gas". W High Resolution Spectroscopy. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/hrs.1993.tha1.
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Carbenes are a significant trace constituent of the gas in the interstellar medium (and in the expanding shell around at least one star), representing about one-sixth of the molecular species that have been identified in space. The identification of one of the most abundant and widespread interstellar carbenes, the cyclopropenylidene ring, C3H2, is described, together with recent laboratory work on the excited vibrational states of this molecule and on the geometrical structure of one of its isomers, the carbon chain carbene H2C3. A number of additional free carbines which might be detected in space are considered. There are at least two reasons why carbenes are comparatively conspicuous in astronomical sources relative to other reactive molecules: one is their high polarity; a second is their production via the same ion-molecule reactions that make known stable species in space (or very similar reactions). Finally, it is pointed out that cumulene carbon chains somewhat longer than those so far detected in space are promising candidates for the carriers of the interstellar optical diffuse bands.