Articoli di riviste: "Interstellar molecules"

1

Winnewisser, G., e E. Herbst. "Interstellar molecules". Reports on Progress in Physics 56, n. 10 (1 ottobre 1993): 1209–73. http://dx.doi.org/10.1088/0034-4885/56/10/001.

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2

Lequeux, J., e E. Roueff. "Interstellar molecules". Physics Reports 200, n. 5 (febbraio 1991): 241–99. http://dx.doi.org/10.1016/0370-1573(91)90010-j.

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3

Kuan, Y. J., H. C. Huang, S. B. Charnley, W. L. Tseng, L. E. Snyder, P. Ehrenfreund, Z. Kisiel, S. Thorwirth, R. K. Bohn e T. L. Wilson. "Prebiologically Important Interstellar Molecules". Symposium - International Astronomical Union 213 (2004): 185–88. http://dx.doi.org/10.1017/s0074180900193246.

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Understanding the organic chemistry of molecular clouds, particularly the formation of biologically important molecules, is fundamental to the study of the processes which lead to the origin, evolution and distribution of life in the Galaxy. Determining the level of molecular complexity attainable in the clouds, and the nature of the complex organic material available to protostellar disks and the planetary systems that form from them, requires an understanding of the possible chemical pathways and is therefore a central question in astrochemistry. We have thus searched for prebiologically important molecules in the hot molecular cloud cores: Sgr B2(N-LMH), W51 e1/e2 and Orion-KL. Among the molecules searched: Pyrimidine is the unsubstituted ring analogue for three of the DNA and RNA bases. 2H-Azirine and Aziridine are azaheterocyclic compounds. And Glycine is the simplest amino acid. Detections of these interstellar organic molecular species will thus have important implications for Astrobiology. Our preliminary results indicate a tentative detection of interstellar glycine. If confirmed, this will be the first detection of an amino acid in interstellar space and will greatly strengthen the thesis that interstellar organic molecules could have played a pivotal role in the prebiotic chemistry of the early Earth.

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4

Kerridge, J. F. "Interstellar Molecules in Meteorites". Symposium - International Astronomical Union 135 (1989): 383–88. http://dx.doi.org/10.1017/s0074180900125392.

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Substantial enrichment of deuterium, D, in certain components of chondritic meteorites is interpreted as a record of isotopic fractionation during ion-molecule reactions at the very low temperatures characteristic of dense interstellar clouds. Whether those meteorites still contain the actual molecules that were synthesised in the presolar interstellar medium, or whether the interstellar material was recycled into a later generation of molecules within the early solar system is not known.

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5

Menten, Karl M. "Interstellar methanol masers". Symposium - International Astronomical Union 206 (2002): 125–26. http://dx.doi.org/10.1017/s0074180900222213.

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The asymmetric rotor molecule methanol (CH3OH) has hundreds of transitions at centimeter-, millimeter-, and submillimeter wavelengths. Many of these are excited in the hot (T ≳ 150 K), dense (n ≳ 106 cm−3) molecular cloud cores surrounding newly formed massive stars or protostars. The high temperatures in these cores cause evaporation of icy grain mantles, releasing copious amounts of complex molecules, such as methanol, in the gas phase, which in hot cores has abundances (up to 10−6 relative to H2) that are two or more orders of magnitude higher than in cold dark clouds.

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6

Kaźmierczak, Maja, Mirosław Schmidt e Jacek Krełowski. "Dicarbon molecule in the interstellar clouds". Proceedings of the International Astronomical Union 4, S251 (febbraio 2008): 45–46. http://dx.doi.org/10.1017/s1743921308021145.

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AbstractWe present high-resolution and high signal-to-noise spectroscopic observations of interstellar molecular lines of C2 towards early-type stars. C2 is particularly interesting because it is the simplest multicarbon molecule and its abundances give information on the chemistry of interstellar clouds, especially on the pathway of formation of (hydro)carbon chains and PAHs which may be considered as possible carriers of diffuse interstellar bands (DIBs). Homonuclear diatomic molecules have negligible dipol moments and hence radiative cooling of excited rotational levels may go only trough the slow quadrupole transitions (van Dishoeck & Black 1982). In C2, pumped by galactic average interstellar field rotational levels are excited effectively much above the gas kinetic temperature and a rotational ladder of electronic transitions is usually observed from high rotational levels. Relations between abundances of the dicarbon and other simple interstellar molecules are considered as well.

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7

Ziurys, L. M., e B. E. Turner. "New Interstellar Molecular Detections: Implications for “Shock Chemistry”". Symposium - International Astronomical Union 120 (1987): 289–92. http://dx.doi.org/10.1017/s0074180900154166.

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Several new interstellar species have recently been detected in the molecular gas, including rotationally-excited CH, vibrationally-excited HCN, and a new molecular ion, HCNH+. These detections have raised some interesting questions concerning the relative importance of “shock” or “high temperature” chemistry vs. ion-molecule reactions in the synthesis of interstellar molecules in dense clouds.

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8

Aiello, S., B. Barsella, C. Cecchi-Pestellini, F. Mencaraglia e A. Rosolia. "Molecular Life-Time against Photodissociation in Dark Interstellar Clouds". Symposium - International Astronomical Union 120 (1987): 75–76. http://dx.doi.org/10.1017/s0074180900153811.

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Molecules in the interstellar space are exposed to interstellar radiation, so that they are destroyed by photodissociation processes, leading to the production of smaller molecules and ions, which in turn can react with other molecular species. Therefore, dissociation rates and dissociation products are important for the chemistry of interstellar molecules. This holds true also for relatively opaque and dense clouds (τ ≲ 10 in the visual), due to the multiple scattering of UV radiation by dust.

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9

Thaddeus, P. "The prebiotic molecules observed in the interstellar gas". Philosophical Transactions of the Royal Society B: Biological Sciences 361, n. 1474 (7 settembre 2006): 1681–87. http://dx.doi.org/10.1098/rstb.2006.1897.

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Over 130 molecules have been identified in the interstellar gas and circumstellar shells, the largest among them is a carbon chain with 13 atoms and molecular weight of 147 (twice that of the simplest amino acid glycine). The high reliability of astronomical identifications, as well as the fairly accurate quantitative analysis which can often be achieved, is emphasized. Glycine itself has been claimed, but a recent analysis indicates that few, if any, of the astronomical radio lines attributed to glycine are actually from that molecule. Polycyclic aromatic hydrocarbons (PAHs) have long been proposed as the source of the unidentified infrared bands between 3 and 16 μm, but no single PAH has been identified in space, partly because PAHs generally have weak or non-existent radio spectra. A remarkable exception is the non-planar corannulene molecule (C 20 H 10 ) that has a strong radio spectrum; in the rich molecular cloud TMC-1, it is found that less than 10 −5 of the carbon is contained in this molecule, suggesting that PAHs are not the dominant large molecules in the interstellar gas, as has been claimed. Owing to inherent spectroscopic limitations, determining the structures of the large molecules in space may require capture of the dust grains, which are continually entering the outer Solar System.

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10

Jose, Jeeno, Alon Zamir e Tamar Stein. "Molecular dynamics reveals formation path of benzonitrile and other molecules in conditions relevant to the interstellar medium". Proceedings of the National Academy of Sciences 118, n. 19 (3 maggio 2021): e2101371118. http://dx.doi.org/10.1073/pnas.2101371118.

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Polycyclic aromatic hydrocarbons and polycyclic aromatic nitrogen heterocycles are believed to be widespread in different areas of the interstellar medium. However, the astronomical detection of specific aromatic molecules is extremely challenging. As a result, only a few aromatic molecules have been identified, and very little is known about how they are formed in different areas of the interstellar medium. Recently, McGuire et al. [Science 359, 202–205 (2018)] detected the simple aromatic molecule benzonitrile in Taurus Molecular Cloud-1. Although benzonitrile has been observed, the molecular mechanism for its formation is still unknown. In this study, we use quantum chemistry and ab initio molecular dynamics to model ionization processes of van der Waals clusters containing cyanoacetylene and acetylene molecules. We demonstrate computationally that the clusters' ionization leads to molecular formation. For pure cyanoacetylene clusters, we observe bond formation among two and three monomer units, whereas in mixed clusters, bond formation can also occur in up to four units. We show that the large amount of energy available to the system after ionization can lead to barrier crossing and the formation of complex molecules. Our study reveals the rich chemistry that is observed upon ionization of the clusters, with a wide variety of molecules being formed. Benzonitrile is among the observed molecules, and we study the potential energy path for its formation. These results also offer insights that can guide astronomers in their search for aromatic molecules in the interstellar medium.

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11

Min, Y. C. "ASTROCHEMISTRY AND INTERSTELLAR MOLECULES". Publications of The Korean Astronomical Society 25, n. 1 (31 marzo 2010): 1–13. http://dx.doi.org/10.5303/pkas.2010.25.1.001.

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12

Smith, Keith T. "Molecules in interstellar space". Science 363, n. 6428 (14 febbraio 2019): 704.7–705. http://dx.doi.org/10.1126/science.363.6428.704-g.

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13

Herbst, Eric, e Ewine F. van Dishoeck. "Complex Organic Interstellar Molecules". Annual Review of Astronomy and Astrophysics 47, n. 1 (settembre 2009): 427–80. http://dx.doi.org/10.1146/annurev-astro-082708-101654.

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14

Candian, Alessandra, e Cameron J. Mackie. "Anharmonic interstellar PAH molecules". International Journal of Quantum Chemistry 117, n. 2 (14 settembre 2016): 146–50. http://dx.doi.org/10.1002/qua.25292.

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15

Saito, Shuji. "Laboratory Microwave Spectroscopy of Interstellar Molecules". Symposium - International Astronomical Union 115 (1987): 92. http://dx.doi.org/10.1017/s0074180900095085.

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One of the main difficulties to identify molecular species in space has been raised by the lack of reliable spectroscopic data for various molecules, especially for chemically active free radicals and molecular ions. Some of the free radicals and molecular ions have been fundamental to the study of chemistry in space but they are too active under terrestrial conditions and are hardly produced in concentrations enough for laboratory observations. We have developed a millimeter-wave spectrometer of high sensitivity suitable for observations of transient molecules. It covers the frequency region of 30 to 410 GHz and has the sensitivity enabling us to detect molecules in a concentration of 107 molecules/cm3 (about 30 ppb). This high sensitivity is achieved by a combination of low noise and high power microwave source, low noise detector, and low loss cell in the high frequency region, assisted by a mini-computer. We have studied various diatomic and polyatomic transient species, some of which may have likely astronomical significance. They are H2D+, PO, PO2, HPO, CCO, HCCN, SiN, FeO, and CH3O.

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16

Mcgonagle, Douglas, William Irvine e Young Minh. "Nitrogen Sulfide (NS) in Star Forming Regions". Symposium - International Astronomical Union 150 (1992): 227–30. http://dx.doi.org/10.1017/s0074180900090070.

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Gas phase models of ion molecule chemistry have been rather successful in matching the observed abundances of small interstellar molecules containing carbon, hydrogen, and oxygen. However, the situation is somewhat less clear for nitrogen-containing species, partly because the important initiating reaction N+ + H2 is slightly endothermic; and for sulfur-containing molecules, where it remains uncertain whether it is necessary to invoke surface reactions on grains to match the observed abundances. As a relatively simple species, the abundance of nitrogen sulfide should provide a good test of the models of the coupled chemistry of nitrogen and sulfur. Until very recently only two molecules containing both these elements were known in the interstellar medium, NS and HNCS, and both have been observed only in Sgr B2. We have therefore undertaken a survey for interstellar NS in Galactic molecular clouds using the FCRAO 14-meter telescope. The 2Π1/2, J = 5/2 → 3/2, transition has in fact been detected in many regions of massive star formation (see table).

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17

Irvine, William M. "Microwave Spectroscopy of Astrophysical Molecules". Highlights of Astronomy 8 (1989): 339–44. http://dx.doi.org/10.1017/s1539299600007966.

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ABSTRACTRecent detections of new molecules in dense interstellar clouds, first detections of certain chemical elements in interstellar molecules, and new information on isotopic fractionation of hydrogen in the interstellar medium are discussed in the context of the need for new laboratory data on transition rest frequencies, reaction rates, and branching ratios.

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18

Winnewisser, Gisbert. "Interstellar Molecules of Prebiotic Interest". International Astronomical Union Colloquium 161 (gennaio 1997): 5–22. http://dx.doi.org/10.1017/s0252921100014573.

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AbstractThe field of interstellar molecules is reviewed with special consideration of molecules which are of potential biological interest. At present more than 110 interstellar molecules have been identified in interstellar clouds and circumstellar envelopes. The more complex molecules are found in the dense cores which are often the sites of active star formation. These locations represent prime targets for the search of larger molecules such as glycine and possibly other amino acids. However, in the list of detected interstellar molecules still many simple hydrides are missing, e.g. SH, PH, PH2, etc., which constitute the building blocks for larger molecules and biomolecules. With the technological opening of the terahertz region to both laboratory and interstellar spectroscopy, great scientific advances are to expected such as the direct detection of the low energy bending vibrations of larger (linear) molecules or the ring-puckering motion of larger ring molecules like the polycyclic (multiring) aromatic hydrocarbons, which might shed new light on the assignment of the «unidentified infrared» features or even on the diffuse visible interstellar bands (DIBs).

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19

Williams, David A. "Chemical Effects of Interstellar Grains". Highlights of Astronomy 8 (1989): 383–86. http://dx.doi.org/10.1017/s1539299600008029.

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ABSTRACTThe chemical effects of interstellar grains are briefly reviewed. Their dominant chemical role is to catalyze the formation of H2 which is the seminal molecule for efficient gas phase chemistry. In regions of at least moderate extinction grains accumulate molecular mantles of CO, H2O, etc. Solid state chemistry in such mantles may produce molecules of a type or in an abundance not achievable in the interstellar gas. Return of mantle material to the gas can – at least transiently – dominate gas phase chemistry. It is argued that the freeze-out of heavy atomic and molecular species on to grain surfaces limits the time available for chemistry, restricts molecular cloud chemistry to a “young” character, and suggests that chemical models of molecular clouds must have cyclic dynamics. Such models are briefly described.

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20

Schmidt, Timothy W., e Robert G. Sharp. "The Optical Spectroscopy of Extraterrestrial Molecules". Australian Journal of Chemistry 58, n. 2 (2005): 69. http://dx.doi.org/10.1071/ch04269.

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The ongoing quest to identify molecules in the interstellar medium by their electronic spectra in the visible region is reviewed. Identification of molecular absorption is described in the context of the elucidation of the carriers of the unidentified Diffuse Interstellar Bands, and molecular emission is discussed with reference to the unidentified Red Rectangle bands. The experimental techniques employed in undertaking studies on the optical spectroscopy of extraterrestrial molecules are described and critiqued in the context of their application.

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21

Abplanalp, Matthew J., Samer Gozem, Anna I. Krylov, Christopher N. Shingledecker, Eric Herbst e Ralf I. Kaiser. "A study of interstellar aldehydes and enols as tracers of a cosmic ray-driven nonequilibrium synthesis of complex organic molecules". Proceedings of the National Academy of Sciences 113, n. 28 (5 luglio 2016): 7727–32. http://dx.doi.org/10.1073/pnas.1604426113.

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Complex organic molecules such as sugars and amides are ubiquitous in star- and planet-forming regions, but their formation mechanisms have remained largely elusive until now. Here we show in a combined experimental, computational, and astrochemical modeling study that interstellar aldehydes and enols like acetaldehyde (CH3CHO) and vinyl alcohol (C2H3OH) act as key tracers of a cosmic-ray-driven nonequilibrium chemistry leading to complex organics even deep within low-temperature interstellar ices at 10 K. Our findings challenge conventional wisdom and define a hitherto poorly characterized reaction class forming complex organic molecules inside interstellar ices before their sublimation in star-forming regions such as SgrB2(N). These processes are of vital importance in initiating a chain of chemical reactions leading eventually to the molecular precursors of biorelevant molecules as planets form in their interstellar nurseries.

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22

Ohishi, Masatoshi. "Molecular spectral line surveys and the organic molecules in the interstellar molecular clouds". Proceedings of the International Astronomical Union 4, S251 (febbraio 2008): 17–26. http://dx.doi.org/10.1017/s174392130802108x.

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AbstractIt is known that more than 140 interstellar and circumstellar molecules have so far been detected, mainly by means of the radio astronomy observations. Many organic molecules are also detected, including alcohols, ketons, ethers, aldehydes, and others, that are distributed from dark clouds and hot cores in the giant molecular clouds. It is believed that most of the organic molecules in space are synthesized through the grain surface reactions, and are evaporated from the grain surface when they are heated up by the UV radiation from adjacent stars.On the other hand the recent claim on the detection of glycine have raised an important issue how difficult it is to confirm secure detection of weak spectra from less abundant organic molecules in the interstellar molecular cloud.I will review recent survey observations of organic molecules in the interstellar molecular clouds, including independent observations of glycine by the 45 m radio telescope in Japan, and will discuss the procedure to securely identify weak spectral lines from organic molecules and the importance of laboratory measurement of organic species.

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23

Adams, Nigel G., e David Smith. "Recent Advances in the studies of Reaction Rates relevant to Interstellar Chemistry". Symposium - International Astronomical Union 120 (1987): 1–18. http://dx.doi.org/10.1017/s0074180900153707.

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The current status of laboratory measurements of the rate coefficients for ionic reactions involved in interstellar molecular synthesis is discussed and the experimental techniques used to acquire such data are briefly described. Examples are given of laboratory data which are being obtained at temperatures close to those of interstellar clouds. Particular attention is given to the results of recent theoretical and experimental work which show that the rate coefficients for the binary reactions of ions with polar molecules at low temperatures are much larger than previously assumed. It is shown how these new developments in experiment and theory are reconciling the differences between predicted and observed abundances for some interstellar molecules. Also briefly discussed are: - the phenomenon of isotope exchange in ion/neutral reactions which explains the apparent enrichment of heavy isotopes in some interstellar molecules, the role of atoms in molecular synthesis, some studies of ion/neutral reactions pertaining to shocked regions of interstellar clouds, ternary association reactions and the analogous radiative association reactions, and recent new laboratory measurements of dissociative recombination coefficients. Finally, some guidance is offered in the proper choice of critical kinetic data for use in interstellar chemical modelling and some further requirements and likely future developments are mentioned.

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24

Kaźmierczak, M., M. Schmidt, T. Weselak, G. Galazutdinov e J. Krełowski. "C2 and Diffuse Interstellar Bands". Proceedings of the International Astronomical Union 9, S297 (maggio 2013): 121–24. http://dx.doi.org/10.1017/s1743921313015718.

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AbstractC2, the simplest multicarbon molecule is a useful astronomical tool, because the analysis of its lines allows to determine the physical conditions in interstellar clouds. C2 abundances give information about the chemistry of interstellar clouds, especially on the pathway to the formation of long-chain carbon molecules, which may be connected with carriers of diffuse interstellar bands (Douglas 1977, Thorburn et al. 2003). Here we summarize all relations between C2 and diffuse interstellar bands (DIBs).

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25

Mitchell, George F. "Chemistry in Shocked Interstellar Gas". Symposium - International Astronomical Union 120 (1987): 275–87. http://dx.doi.org/10.1017/s0074180900154154.

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In its passage through the interstellar gas, a shock imposes massive and irreversible changes on the chemical composition of the gas. The synthesis of molecules from atoms and atomic ions can be highly efficient behind non-dissociative (i.e. slow) shocks. Results of kinetic calculations behind non-dissociative shocks are reviewed here, with emphasis given to the dependence of the postshock molecular composition on initial cloud properties. It is shown that a dense cloud shock can convert essentially all neutral atoms into various molecules. Even in diffuse and unshielded regions, a variety of molecules can attain a high abundance behind shocks. The suggestion that the widespread diffuse cloud species CH+ is shock synthesized is critically examined in the light of new calculations.

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26

Gredel, R., S. Lepp, A. Dalgarno e E. Herbst. "Cosmic Ray Induced Photodestruction of Interstellar Molecules". International Astronomical Union Colloquium 120 (1989): 32–37. http://dx.doi.org/10.1017/s0252921100023459.

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AbstractUltraviolet photons are created in the interior of dense interstellar clouds by the impact excitation of molecular hydrogen by secondary electrons generated by cosmic ray ionization. The resulting photodissociation and photoionization rates of a wide range of interstellar molecules are calculated. The effects on the equilibrium chemical composition of dense clouds are briefly discussed.

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27

Gerin, M., F. Levrier, E. Falgarone, B. Godard, P. Hennebelle, F. Le Petit, M. De Luca et al. "Hydride spectroscopy of the diffuse interstellar medium: new clues on the gas fraction in molecular form and cosmic ray ionization rate in relation to H 3 +". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, n. 1978 (13 novembre 2012): 5174–85. http://dx.doi.org/10.1098/rsta.2012.0023.

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The Herschel-guaranteed time key programme PRobing InterStellar Molecules with Absorption line Studies (PRISMAS) 1 is providing a survey of the interstellar hydrides containing the elements C, O, N, F and Cl. As the building blocks of interstellar molecules, hydrides provide key information on their formation pathways. They can also be used as tracers of important physical and chemical properties of the interstellar gas that are difficult to measure otherwise. This paper presents an analysis of two sight-lines investigated by the PRISMAS project, towards the star-forming regions W49N and W51. By combining the information extracted from the detected spectral lines, we present an analysis of the physical properties of the diffuse interstellar gas, including the electron abundance, the fraction of gas in molecular form, and constraints on the cosmic ray ionization rate and the gas density.

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Belloche, Arnaud. "Molecular complexity in the interstellar medium". Proceedings of the International Astronomical Union 15, S350 (aprile 2019): 96–99. http://dx.doi.org/10.1017/s1743921319006380.

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AbstractThe search for complex organic molecules in the interstellar medium (ISM) has revealed species of ever greater complexity. This search relies on the progress made in the laboratory to characterize their rotational spectra. Our understanding of the processes that lead to molecular complexity in the ISM builds on numerical simulations that use chemical networks fed by laboratory and theoretical studies. The advent of ALMA and NOEMA has opened a new door to explore molecular complexity in the ISM. Their high angular resolution reduces the spectral confusion of star-forming cores and their increased sensitivity allows the detection of low-abundance molecules that could not be probed before. The complexity of the recently-detected molecules manifests itself not only in terms of number of atoms but also in their molecular structure. We discuss these developments and report on ReMoCA, a new spectral line survey performed with ALMA toward the high-mass star-forming region Sgr B2(N).

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Ter Meulen, J. J. "Inelastic collisions of interstellar molecules". Symposium - International Astronomical Union 178 (1997): 241–52. http://dx.doi.org/10.1017/s0074180900009396.

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The rotational energy transfer of NH3, OH and D2CO in inelastic collisions with He and H2 is studied in a crossed molecular beam experiment. The molecules are prepared in a single initial state by rotational cooling in an adiabatic expansion followed by electrostatic state selection. Relative state-to-state cross sections are determined by measuring the collision induced redistribution of the population of the initial state by using state selective laser detection techniques. The results for NH3 and OH are compared to theoretical values obtained from quantum calculations. Except for NH3 — He where theory predicts a parity selection rule for transitions to the 33 and 43 states, which is not observed in the experiment, good agreement between experiment and theory is obtained.

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Shingledecker, C. N., K. L. K. Lee, J. T. Wandishin, N. Balucani, A. M. Burkhardt, S. B. Charnley, R. Loomis et al. "Detection of interstellar H2CCCHC3N". Astronomy & Astrophysics 652 (agosto 2021): L12. http://dx.doi.org/10.1051/0004-6361/202140698.

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Context. The chemical pathways linking the small organic molecules commonly observed in molecular clouds to the large, complex, polycyclic species long suspected of being carriers of the ubiquitous unidentified infrared emission bands remain unclear. Aims. To investigate whether the formation of mono- and polycyclic molecules observed in cold cores could form via the bottom-up reaction of ubiquitous carbon-chain species with, for example, atomic hydrogen, a search is made for possible intermediates in data taken as part of the GOTHAM (GBT Observations of TMC-1: Hunting for Aromatic Molecules) project. Methods. Markov chain Monte Carlo (MCMC) source models were run to obtain column densities and excitation temperatures. Astrochemical models were run to examine possible formation routes, including (a) a novel grain-surface pathway involving the hydrogenation of C6N and HC6N, (b) purely gas-phase reactions between C3N and both propyne (CH3CCH) and allene (CH2CCH2), and (c) via the reaction CN + H2CCCHCCH. Results. We report the first detection of cyanoacetyleneallene (H2CCCHC3N) in space toward the TMC-1 cold cloud using the Robert C. Byrd 100 m Green Bank Telescope. Cyanoacetyleneallene may represent an intermediate between less-saturated carbon chains, such as the cyanopolyynes, that are characteristic of cold cores and the more recently discovered cyclic species, such as cyanocyclopentadiene. Results from our models show that the gas-phase allene-based formation route in particular produces abundances of H2CCCHC3N that match the column density of 2 × 1011 cm−2 obtained from the MCMC source model, and that the grain-surface route yields large abundances on ices that could potentially be important as precursors for cyclic molecules.

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Smith, Peter L. "Oscillator Strengths for Visible and Ultraviolet Observations of Interstellar Molecules". Symposium - International Astronomical Union 120 (1987): 95–102. http://dx.doi.org/10.1017/s0074180900153872.

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The accuracy of the information obtained from observations of optical-wavelength, molecular absorption features in interstellar clouds is directly limited by the accuracy of the rotational-line oscillator strengths used in the analysis of data. This paper briefly discusses optical observations of molecules in interstellar clouds; surveys molecular lifetime and oscillator strengths; and reviews laboratory techniques for obtaining these data.

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Szczepanski, J., e M. Vala. "Vibrational spectroscopy of interstellar molecules". European Physical Journal Special Topics 144, n. 1 (maggio 2007): 27–40. http://dx.doi.org/10.1140/epjst/e2007-00106-y.

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Tielens, A. G. G. M. "Interstellar Polycyclic Aromatic Hydrocarbon Molecules". Annual Review of Astronomy and Astrophysics 46, n. 1 (settembre 2008): 289–337. http://dx.doi.org/10.1146/annurev.astro.46.060407.145211.

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Snow, Theodore P. "Ultraviolet Observations of Interstellar Molecules". Proceedings of the International Astronomical Union 1, S231 (21 marzo 2006): 175. http://dx.doi.org/10.1017/s1743921306007174.

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Furuya, Kenji. "Isotopic fractionation in interstellar molecules". Proceedings of the International Astronomical Union 13, S332 (marzo 2017): 163–74. http://dx.doi.org/10.1017/s1743921317006810.

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AbstractThe level of isotopic fractionation in molecules provides insights into their formation environments and how they formed. In this article, we review hydrogen and nitrogen isotopic fractionation in low-mass star-forming regions. Interstellar molecules are significantly enriched in deuterium. The importance of the nuclear spin states of light species on deuterium fractionation and the usefulness of singly and doubly deuterated molecules as chemical tracers are discussed. Observations have revealed that molecules in prestellar cores are enriched in or depleted in15N depending on molecules. Compared with deuterium fractionation chemistry, our understanding of15N fractionation chemistry is not well established. We briefly discuss potential15N fractionation routes, i.e., isotopic-exchange reactions and isotopic selective photodissociation of N2. In addition, the selective freeze-out of15N atoms onto dust grains around the transition between N atoms and N2is discussed as a potential mechanism that causes the depletion of15N in the gas phase.

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Wootten, Alwyn. "Deuterated Molecules in Interstellar Clouds". Symposium - International Astronomical Union 120 (1987): 311–19. http://dx.doi.org/10.1017/s0074180900154221.

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We show that deuteration in DCN and HDCO probably derives from CH2D+ in warm clouds, and that the levels of deuteration observed in those clouds require that radiative association play an important role in the chemistry of interstellar clouds.

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37

Brown, Ronald D. "Prebiotic Matter in Interstellar Molecules". Symposium - International Astronomical Union 112 (1985): 123–37. http://dx.doi.org/10.1017/s0074180900146431.

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With the discovery of the first polyatomic molecules, NH3, H2O and H2CO in 1968/9 there was immediate speculation as to how far biological chemical evolution - from atoms to small carbon compounds of biological significance - could have occurred in the Galaxy. There was also potential conflict with the canonical scientific view of the origin of life, traceable to the production of simple bio-molecules from the influence of energetic atmospheric events on the simple gaseous mixture (CH4, H2, H2O and NH3) presumed to compose the atmosphere of the very young Earth.

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38

Hjalmarson, Åke. "Organic molecules in interstellar space". Acta Astronautica 14 (gennaio 1986): 267–75. http://dx.doi.org/10.1016/0094-5765(86)90128-1.

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39

Kurtadikar, Mukund L., e Suresh C. Mehrotra. "Collisional excitation of interstellar molecules". Astrophysics and Space Science 197, n. 1 (1992): 3–15. http://dx.doi.org/10.1007/bf00645068.

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40

Williams, D. A. "The Role of Grains in Interstellar Chemistry". Symposium - International Astronomical Union 120 (1987): 531–38. http://dx.doi.org/10.1017/s0074180900154567.

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Grains affect interstellar chemistry in a variety of ways. Most obviously, they extinguish starlight and thus protect molecules in cloud interiors from photodestruction. The grains themselves contain substantial proportions of particular elements which are therefore less readily available for gas phase reactions and for processing into molecules. Grains in dense clouds are known to accrete molecular mantles which may be further processed; the mantle material is ultimately returned to the gas, either near hot stars or when the clouds are dissipated. Molecular hydrogen, the key to all gas phase chemistry, is undoubtedly formed efficiently on grains, and a plausible mechanism can now be identified. Other molecules, too, form preferentially at surfaces. Finally, the destruction of grains via chemical erosion and by sputtering in shocks provides a substantial molecular contribution to the gas in local regions.

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41

Snyder, Lewis E. "Cometary Molecules". Symposium - International Astronomical Union 150 (1992): 427–34. http://dx.doi.org/10.1017/s0074180900090598.

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42

Zhang, Yong. "Molecular studies of Planetary Nebulae". Proceedings of the International Astronomical Union 12, S323 (ottobre 2016): 141–49. http://dx.doi.org/10.1017/s1743921317000497.

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AbstractCircumstellar envelopes (CEs) around evolved stars are an active site for the production of molecules. After evolving through the Asymptotic Giant Branch (AGB), proto-planetary nebula (PPN), to planetary nebula (PN) phases, CEs ultimately merge with the interstellar medium (ISM). The study of molecules in PNe, therefore, is essential to understanding the transition from stellar to interstellar materials. So far, over 20 molecular species have been discovered in PNe. The molecular composition of PNe is rather different from those of AGB and PPNe, suggesting that the molecules synthesized in PN progenitors have been heavily processed by strong ultraviolet radiation from the central star. Intriguingly, fullerenes and complex organic compounds having aromatic and aliphatic structures can be rapidly formed and largely survive during the PPN/PN evolution. The similar molecular compositions in PNe and diffuse clouds as well as the detection of C60+ in the ISM reinforce the view that the mass-loss from PNe can significantly enrich the ISM with molecular species, some of which may be responsible for the diffuse interstellar bands. In this contribution, I briefly summarize some recent observations of molecules in PNe, with emphasis on their implications on circumstellar chemistry.

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43

Suzuki, H., M. Ohishi, M. Morimoto, N. Kaifu, P. Friberg, W. M. Irvine, H. E. Matthews e S. Saito. "Recent Observations of Organic Molecules in Nearby Cold, Dark Interstellar Clouds". Symposium - International Astronomical Union 112 (1985): 139–44. http://dx.doi.org/10.1017/s0074180900146443.

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We report recent investigations of the organic chemistry of relatively nearby cold, dark interstellar clouds. Specifically, we confirm the presence of interstellar tricarbon monoxide (C3O) in Taurus Molecular Cloud1 (TMC-1); report the first detection in such regions of acetaldehyde (CH3CHO), the most complex oxygen-containing organic molecule yet found in dark clouds; report the first astronomical detection of several molecular rotational transitions, including the J=18−17 and 14−13 transitions of cyanodiacetylene (HC5N), the 101−000 transition of acetaldehyde, and the J=5−4 transition of C3O; and set a significant upper limit on the abundance of cyanocarbene (HCCN) as a result of the first reported interstellar search for this molecule.

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44

Miksch, April M., Annalena Riffelt, Ricardo Oliveira, Johannes Kästner e Germán Molpeceres. "Hydrogenation of small aromatic heterocycles at low temperatures". Monthly Notices of the Royal Astronomical Society 505, n. 3 (27 maggio 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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45

Omont, Alain. "Chemical Properties of Interstellar Polycyclic Aromatic Molecules". Symposium - International Astronomical Union 120 (1987): 545–46. http://dx.doi.org/10.1017/s0074180900154580.

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Abstract (sommario):

There is substantial evidence of the presence of polycyclic aromatic molecules, mainly hydrocarbons (PAH's) in the interstellar medium (Léger and Puget, 1984, Allamandola et al. 1985, Léger and d'Hendecourt in these proceedings). They should contain typically NC = 20–100 carbon atoms, and they can contain perhaps 1–10% of the total interstellar carbon. I have recently discussed in detail their physical and chemical properties (Omont, 1986), which should be intermediate between that of conventional interstellar molecules and grains.

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46

Hu, Xiaoyi, Yuanyuan Yang, Congcong Zhang, Yang Chen, Junfeng Zhen e Liping Qin. "Gas-phase laboratory formation of large, astronomically relevant PAH-organic molecule clusters". Astronomy & Astrophysics 656 (dicembre 2021): A80. http://dx.doi.org/10.1051/0004-6361/202141407.

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Polycyclic aromatic hydrocarbon (PAH) molecules may play an essential role in the prebiotic compound evolution network in interstellar clouds. In this work, an experimental study of large, astronomically relevant PAH-organic molecule clusters is presented. With the initial molecular precursors dicoronylene (DC; C48H20)-pyroglutamic acid (Pga, C5H7NO3), DC-proline (Pro; C5H9NO2), and DC-pyroglutaminol (Pgn; C5H9NO2), our experiments indicate that PAH–organic molecule cluster cations (e.g., (Pga)(1−2)C48Hn+, (Pro)(1−2)C48Hn+, and (Pgn)(1−6)C48Hn+) and carbon cluster–organic molecule cluster cations (e.g., (Pga)C48+, (Pro)(1−2)C48+, and (Pgn)(1−6)C48+) are gradually formed through an ion-molecule collision reaction pathway in the presence of a strong galactic interstellar radiation field. These laboratory studies provide a gas-phase growth route toward the formation of complex prebiotic compounds in a bottom-up growth process, as well as insight into their chemical-evolution behavior in the interstellar medium.

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47

Ehrenfreund, Pascale. "Composition of Comets and Interstellar Dust". Highlights of Astronomy 12 (2002): 229–32. http://dx.doi.org/10.1017/s1539299600013332.

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AbstractRecent observational results from ground and space-based observatories in combination with laboratory simulations allow us to monitor the evolution, survival, transport and transformation of cosmic dust from molecular clouds and the diffuse interstellar medium, until their incorporation into Solar System material. The composition of comets encodes information on their origin and can be used as a tracer for processes which were predominant in the protosolar nebula. A comparison of the composition and abundances of interstellar molecules and cometary volatiles reveals a general correspondence, but discrepancies are also apparent. Detailed studies indicate that cometary ices are a mixture of original interstellar material with material that has been moderately to heavily processed in the pre-solar nebula. The inventory and distribution of ice and organic molecules in interstellar clouds and in comets and their common link are briefly described.

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48

Sanz-Novo, Miguel, Víctor M. Rivilla, Holger S. P. Müller, Izaskun Jiménez-Serra, Jesús Martín-Pintado, Laura Colzi, Shaoshan Zeng et al. "Discovery of Thionylimide, HNSO, in Space: The first N-, S-, and O-bearing Interstellar Molecule". Astrophysical Journal Letters 965, n. 2 (1 aprile 2024): L26. http://dx.doi.org/10.3847/2041-8213/ad3945.

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Abstract We present the first detection in space of thionylimide (HNSO) toward the Galactic center molecular cloud G + 0.693-0.027, thanks to the superb sensitivity of an ultradeep molecular line survey carried out with the Yebes 40 m and IRAM 30 m telescopes. This molecule is the first species detected in the interstellar medium containing, simultaneously, N, S, and O. We have identified numerous K a = 0, 1, and 2 transitions belonging to HNSO covering from J up = 2 to J up =10, including several completely unblended features. We derive a molecular column density of N = (8 ± 1)×1013 cm−2, yielding a fractional abundance relative to H2 of ∼6 × 10−10, which is about ∼37 and ∼4.8 times less abundant than SO and SO2, respectively. Although there are still many unknowns in the interstellar chemistry of NSO-bearing molecules, we propose that HNSO is likely formed through the reaction of the NSO radical and atomic H on the surface of icy grains, with alternative routes also deserving exploration. Finally, HNSO appears as a promising link between N, S, and O interstellar chemistry, and its discovery paves the route to the detection of a new family of molecules in space.

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49

Toscano, Jutta. "Rotational-state-selected Carbon Astrochemistry". CHIMIA 78, n. 1/2 (28 febbraio 2024): 40–44. http://dx.doi.org/10.2533/chimia.2024.40.

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The addition of individual quanta of rotational excitation to a molecule has been shown to markedly change its reactivity by significantly modifying the intermolecular interactions. So far, it has only been possible to observe these rotational effects in a very limited number of systems due to lack of rotational selectivity in chemical reaction experiments. The recent development of rotationally controlled molecular beams now makes such investigations possible for a wide range of systems. This is particularly crucial in order to understand the chemistry occurring in the interstellar medium, such as exploring the formation of carbon-based astrochemical molecules and the emergence of molecular complexity in interstellar space from the reaction of small atomic and molecular fragments.

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50

Snow, Theodore P. "The Diffuse Interstellar Bands And Organic Molecules In Space". International Astronomical Union Colloquium 161 (gennaio 1997): 49–59. http://dx.doi.org/10.1017/s0252921100014597.

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AbstractThe diffuse interstellar bands have been recognized for over 75 years, and remain unidentified today. This family of broad interstellar absorption features, now numbering well over 100, has been the subject of a great deal of speculation, intensive observations, and lately has stimulated the interest of chemists as well as astronomers. In this review I briefly summarize the history of the problem and then provide an overview of the current state of affairs. I emphasize recent evidence that the carriers are large molecular species, most likely organic in nature, which are abundant in the diffuse interstellar medium. If so, then the ultimate identification of the responsible species will provide a new window into the detailed chemical and physical properties of the interstellar gas. I also discuss constraints imposed on the carriers by a recent reassessment of the interstellar carbon abundance.

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