Articles de revues : « Interstellar Atmosphere Chemistry »

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Phillips, T. G., Ewine F. Van Dishoeck et Jocelyn B. Keene. « Interstellar H3O+ ». Symposium - International Astronomical Union 150 (1992) : 191–92. http://dx.doi.org/10.1017/s0074180900089993.

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The H3O+ ion is a key species in the oxygen chemistry leading to H2O, OH and O2. Chemical models predict O2 and H2O to be the dominant oxygen-bearing molecules in interstellar clouds. However, neither of them can easily be observed in the bulk of the interstellar medium because of blockage from the Earth's atmosphere. Determination of the abundance and distribution of the precursor H3O+ ion might thus provide an important indirect measure of their abundances.

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Peacock, Sarah, Travis S. Barman, Adam C. Schneider, Michaela Leung, Edward W. Schwieterman, Evgenya L. Shkolnik et R. O. Parke Loyd. « Accurate Modeling of Lyα Profiles and Their Impact on Photolysis of Terrestrial Planet Atmospheres ». Astrophysical Journal 933, n^o 2 (1 juillet 2022) : 235. http://dx.doi.org/10.3847/1538-4357/ac77f2.

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Abstract Accurately measuring and modeling the Lyα (Lyα; λ1215.67 Å) emission line from low-mass stars is vital for our ability to build predictive high energy stellar spectra, yet interstellar medium (ISM) absorption of this line typically prevents model-measurement comparisons. Lyα also controls the photodissociation of important molecules, like water and methane, in exoplanet atmospheres such that any photochemical models assessing potential biosignatures or atmospheric abundances require accurate Lyα host star flux estimates. Recent observations of three early M and K stars (K3, M0, M1) with exceptionally high radial velocities (>100 km s−1) reveal the intrinsic profiles of these types of stars as most of their Lyα flux is shifted away from the geocoronal line core and contamination from the ISM. These observations indicate that previous stellar spectra computed with the PHOENIX atmosphere code have underpredicted the core of Lyα in these types of stars. With these observations, we have been able to better understand the microphysics in the upper atmosphere and improve the predictive capabilities of the PHOENIX atmosphere code. Since these wavelengths drive the photolysis of key molecular species, we also present results analyzing the impact of the resulting changes to the synthetic stellar spectra on observable chemistry in terrestrial planet atmospheres.

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Barnett, NeilW. « Spectroscopy of the Earth's Atmosphere and Interstellar Medium ». Analytica Chimica Acta 284, n^o 1 (décembre 1993) : 241. http://dx.doi.org/10.1016/0003-2670(93)80030-o.

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Willacy, Karen, SiHe Chen, Danica J. Adams et Yuk L. Yung. « Vertical Distribution of Cyclopropenylidene and Propadiene in the Atmosphere of Titan ». Astrophysical Journal 933, n^o 2 (1 juillet 2022) : 230. http://dx.doi.org/10.3847/1538-4357/ac6b9d.

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Abstract Titan’s atmosphere is a natural laboratory for exploring the photochemical synthesis of organic molecules. Significant recent advances in the study of the atmosphere of Titan include: (a) detection of C3 molecules: C3H6, CH2CCH2, c-C3H2, and (b) retrieval of C6H6, which is formed primarily via C3 chemistry, from Cassini Ultraviolet Imaging Spectrograph data. The detection of c-C3H2 is of particular significance as ring molecules are of great astrobiological importance. Using the Caltech/JPL KINETICS code, along with the best available photochemical rate coefficients and parameterized vertical transport, we are able to account for the recent observations. It is significant that ion chemistry, reminiscent of that in the interstellar medium, plays a major role in the production of c-C3H2 above 1000 km.

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Smith, David, et Patrik Spanel. « Ions in the terrestrial atmosphere and in interstellar clouds ». Mass Spectrometry Reviews 14, n^o 4-5 (juillet 1995) : 255–78. http://dx.doi.org/10.1002/mas.1280140403.

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Rimmer, Paul B., Catherine Walsh et Christiane Helling. « Cosmic Rays, UV Photons, and Haze Formation in the Upper Atmospheres of Hot Jupiters ». Proceedings of the International Astronomical Union 8, S299 (juin 2013) : 303–4. http://dx.doi.org/10.1017/s1743921313008703.

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AbstractCosmic ray ionization has been found to be a dominant mechanism for the formation of ions in dense interstellar environments. Cosmic rays are further known to initiate the highly efficient ion-neutral chemistry within star forming regions. In this talk we explore the effect of both cosmic rays and UV photons on a model hot Jupiter atmosphere using a non-equlibrium chemical network that combines reactions from the UMIST Database for Astrochemistry, the KIDA database for interstellar and protoplanetary environments and three-body and combustion reactions from the NIST database and from various irradiated gas planet networks. The physical parameters for our model atmosphere are based on HD 189733 b (Effective Temperature of 1000 K, log g = 3.3, solar metallicity, at a distance 0.03 AU from a K dwarf). The active UV photochemistry high in our model hot Jupiter atmosphere tends to destroy these hydrocarbons, but on a time-scale sufficiently slow that PAH formation could already have taken place. In most cases, carbon-bearing species formed by cosmic rays are destroyed by UV photons (e.g. C2H2, C2H4, HC3N). Conversely, carbon-bearing species enhanced by an active photochemistry are depleted when cosmic ray ionization is significant (e.g. CN, HCN and CH4). Ammonia is an interesting exception to this trend, enhanced both by an active photochemistry and a high cosmic ray ionization rate.

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Malmqvist, Per-Åke. « The RASSCF, RASSI, and CASPT2 Methods Used on Small Molecules of Astrophysical Interest ». International Astronomical Union Colloquium 146 (1994) : 338–52. http://dx.doi.org/10.1017/s0252921100021448.

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To a quantum chemist with no particular background in astrophysics or astronomy, a brief glance at journals and textbooks in these fields shows at least three areas where computational quantum chemistry has had a valuable impact: Interstellar cloud chemistry; stellar atmosphere modelling; and chemistry in extreme conditions, such as at the surface of a neutron star. The first two uses are particularly suitable, since standard methods are directly applicable.For such problems, good calculations of potential energy as well as expectation values and matrix elements of dipole and other operators appears to be in demand. Many electronic states may be involved, at least a broad range of problems involve fairly small molecules, often radicals, and conformation regions far from equilibrium. Such problems are addressed by three methods originated in our laboratory, and known by the acronyms RASSCF (Restricted Active Space Self-Consistent Field, Malmqvist et al. 1990), RASSI (RAS State Interaction) and CASPT2 (Complete Active Space Perturbation Theory to Second Order-Complete Active Space Perturbation Theory to Second Order, Andersson et al. 1990; Andersson et al. 1992).

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Notsu, Shota, Christian Eistrup, Catherine Walsh et Hideko Nomura. « The composition of hot Jupiter atmospheres assembled within chemically evolved protoplanetary discs ». Monthly Notices of the Royal Astronomical Society 499, n^o 2 (25 septembre 2020) : 2229–44. http://dx.doi.org/10.1093/mnras/staa2944.

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ABSTRACT The radial-dependent positions of snowlines of abundant oxygen- and carbon-bearing molecules in protoplanetary discs will result in systematic radial variations in the carbon-to-oxygen (C/O) ratios in the gas and ice. This variation is proposed as a tracer of the formation location of gas-giant planets. However, disc chemistry can affect the C/O ratios in the gas and ice, thus potentially erasing the chemical fingerprint of snowlines in gas-giant atmospheres. We calculate the molecular composition of hot Jupiter atmospheres using elemental abundances extracted from a chemical kinetics model of a disc mid-plane, where we have varied the initial abundances and ionization rates. The models predict a wider diversity of possible atmospheres than those predicted using elemental ratios from snowlines only. As found in previous work, as the C/O ratio exceeds the solar value, the mixing ratio of CH4 increases in the lower atmosphere, and those of C2H2 and HCN increase mainly in the upper atmosphere. The mixing ratio of H2O correspondingly decreases. We find that hot Jupiters with C/O > 1 can only form between the CO2 and CH4 snowlines. Moreover, they can only form in a disc which has fully inherited interstellar abundances, and where negligible chemistry has occurred. Hence, carbon-rich planets are likely rare, unless efficient transport of hydrocarbon-rich ices via pebble drift to within the CH4 snowline is a common phenomenon. We predict combinations of C/O ratios and elemental abundances that can constrain gas-giant planet formation locations relative to snowline positions, and that can provide insight into the disc chemical history.

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Bergin, Edwin A., Geoffrey A. Blake, Fred Ciesla, Marc M. Hirschmann et Jie Li. « Tracing the ingredients for a habitable earth from interstellar space through planet formation ». Proceedings of the National Academy of Sciences 112, n^o 29 (6 juillet 2015) : 8965–70. http://dx.doi.org/10.1073/pnas.1500954112.

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We use the C/N ratio as a monitor of the delivery of key ingredients of life to nascent terrestrial worlds. Total elemental C and N contents, and their ratio, are examined for the interstellar medium, comets, chondritic meteorites, and terrestrial planets; we include an updated estimate for the bulk silicate Earth (C/N = 49.0 ± 9.3). Using a kinetic model of disk chemistry, and the sublimation/condensation temperatures of primitive molecules, we suggest that organic ices and macromolecular (refractory or carbonaceous dust) organic material are the likely initial C and N carriers. Chemical reactions in the disk can produce nebular C/N ratios of ∼1–12, comparable to those of comets and the low end estimated for planetesimals. An increase of the C/N ratio is traced between volatile-rich pristine bodies and larger volatile-depleted objects subjected to thermal/accretional metamorphism. The C/N ratios of the dominant materials accreted to terrestrial planets should therefore be higher than those seen in carbonaceous chondrites or comets. During planetary formation, we explore scenarios leading to further volatile loss and associated C/N variations owing to core formation and atmospheric escape. Key processes include relative enrichment of nitrogen in the atmosphere and preferential sequestration of carbon by the core. The high C/N bulk silicate Earth ratio therefore is best satisfied by accretion of thermally processed objects followed by large-scale atmospheric loss. These two effects must be more profound if volatile sequestration in the core is effective. The stochastic nature of these processes hints that the surface/atmospheric abundances of biosphere-essential materials will likely be variable.

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Wang, Zhe-Chen, Callie A. Cole, Nicholas J. Demarais, Theodore P. Snow et Veronica M. Bierbaum. « Reactions of Azine Anions with Nitrogen and Oxygen Atoms : Implications for Titan’s Upper Atmosphere and Interstellar Chemistry ». Journal of the American Chemical Society 137, n^o 33 (17 août 2015) : 10700–10709. http://dx.doi.org/10.1021/jacs.5b06089.

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Jacovella, Ugo, Christopher S. Hansen, Alexandre Giuliani, Adam J. Trevitt et Laurent Nahon. « UV/VUV photoprocessing of protonated N-hetero(poly)acenes ». Monthly Notices of the Royal Astronomical Society 511, n^o 4 (24 février 2022) : 5656–60. http://dx.doi.org/10.1093/mnras/stac496.

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ABSTRACT N-heterocycles are suspected to play an important role in the chemical origin of life. Despite their detection in meteorites and in Titan’s atmosphere, their extra-terrestrial chemical formation networks remain elusive. Furthermore N-heterocyclics are undetected in the interstellar medium. This paper assesses the photostability of protonated N-hetero(poly)acenes after ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. It provides information on their ability to retain the N atom into the cycle to generate larger N-containing species or functionalized N-heterocyles. Protonated N-hetero(poly)acenes were generated using electrospray ionization and injected into a linear ion trap where they were irradiated by radiation of 4.5 to 10 eV using the DESIRS beamline at the synchrotron SOLEIL. The photodissociation action spectra of protonated pyridine, quinoline, isoquinoline, and acridine were measured by recording the photofragment yields as a function of photon energy. The four systems exhibit dissociation channels associated with H2 and HCN/HNC loss but with different branching ratios. The results indicate that increasing the size of the N-hetero(poly)acenes increases the chance of retaining the N atom in the larger fragment ion after photodissociation but it remains that all the protonated N-hetero(poly)acenes studied lose their N atom at part of a small neutral photofragment, with high propensity. Therefore, protonated N-hetero(poly)acenes in interstellar space are unlikely precursors to form larger N-containing species. However, protonated pyridine, quinoline, isoquinoline, and acridine are most likely to retain their N atoms in planetary atmospheres where UV radiation at the planet’s surface is typically restricted to wavelengths greater than 200 nm – suggesting such environments are possible substrates for prebiotic chemistry.

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Casasayas-Barris, N., E. Pallé, F. Yan, G. Chen, S. Kohl, M. Stangret, H. Parviainen et al. « Atmospheric characterization of the ultra-hot Jupiter MASCARA-2b/KELT-20b ». Astronomy & ; Astrophysics 628 (26 juillet 2019) : A9. http://dx.doi.org/10.1051/0004-6361/201935623.

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Ultra-hot Jupiters orbit very close to their host star and consequently receive strong irradiation, causing their atmospheric chemistry to be different from the common gas giants. Here, we have studied the atmosphere of one of these particular hot planets, MASCARA-2b/KELT-20b, using four transit observations with high resolution spectroscopy facilities. Three of these observations were performed with HARPS-N and one with CARMENES. Additionally, we simultaneously observed one of the transits with MuSCAT2 to monitor possible spots in the stellar surface. At high resolution, the transmission residuals show the effects of Rossiter-McLaughlin and centre-to-limb variations from the stellar lines profiles, which we have corrected to finally extract the transmission spectra of the planet. We clearly observe the absorption features of CaII, FeII, NaI, Hα, and Hβ in the atmosphere of MASCARA-2b, and indications of Hγ and MgI at low signal-to-noise ratio. In the case of NaI, the true absorption is difficult to disentangle from the strong telluric and interstellar contamination. The results obtained with CARMENES and HARPS-N are consistent, measuring an Hα absorption depth of 0.68 ± 0.05 and 0.59 ± 0.07%, and NaI absorption of 0.11 ± 0.04 and 0.09 ± 0.05% for a 0.75 Å passband, in the two instruments respectively. The Hα absorption corresponds to ~1.2 Rp, which implies an expanded atmosphere, as a result of the gas heating caused by the irradiation received from the host star. For Hβ and Hγ only HARPS-N covers this wavelength range, measuring an absorption depth of 0.28 ± 0.06 and 0.21 ± 0.07%, respectively. For CaII, only CARMENES covers this wavelength range measuring an absorption depth of 0.28 ± 0.05, 0.41 ± 0.05 and 0.27 ± 0.06% for CaII λ8498Å, λ8542Å and λ8662Å lines, respectively. Three additional absorption lines of FeII are observed in the transmission spectrum by HARPS-N (partially covered by CARMENES), measuring an average absorption depth of 0.08 ± 0.04% (0.75 Å passband). The results presented here are consistent with theoretical models of ultra-hot Jupiters atmospheres, suggesting the emergence of an ionised gas on the day-side of such planets. Calcium and iron, together with other elements, are expected to be singly ionised at these temperatures and be more numerous than its neutral state. The Calcium triplet lines are detected here for the first time in transmission in an exoplanet atmosphere.

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Wang, Zhe-Chen, et Veronica M. Bierbaum. « Reactions of substituted benzene anions with N and O atoms : Chemistry in Titan’s upper atmosphere and the interstellar medium ». Journal of Chemical Physics 144, n^o 21 (7 juin 2016) : 214304. http://dx.doi.org/10.1063/1.4952454.

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Marty, Bernard. « Origins and Early Evolution of the Atmosphere and the Oceans ». Geochemical Perspectives 9, n^o 2 (octobre 2020) : 135–313. http://dx.doi.org/10.7185/geochempersp.9.2.

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My journey in science began with the study of volcanic gases, sparking an interest in the origin, and ultimate fate, of the volatile elements in the interior of our planet. How did these elements, so crucial to life and our surface environment, come to be sequestered within the deepest regions of the Earth, and what can they tell us about the processes occurring there? My approach has been to establish geochemical links between the noble gases, physical tracers par excellence, with major volatile elements of environmental importance, such as water, carbon and nitrogen, in mantle-derived rocks and gases. From these analyses we have learned that the Earth is relatively depleted in volatile elements when compared to its potential cosmochemical ancestors (e.g., ~2 ppm nitrogen compared to several hundreds of ppm in primitive meteorites) and that natural fluxes of carbon are two orders of magnitude lower than those emitted by current anthropogenic activity. Further insights into the origin of terrestrial volatiles have come from space missions that documented the composition of the proto-solar nebula and the outer solar system. The consensus behind the origin of the atmosphere and the oceans is evolving constantly, although recently a general picture has started to emerge. At the dawn of the solar system, the volatile-forming elements (H, C, N, noble gases) that form the majority of our atmosphere and oceans were trapped in solid dusty phases (mostly in ice beyond the snowline and organics everywhere). These phases condensed from the proto-solar nebula gas, and/or were inherited from the interstellar medium. These accreted together within the next few million years to form the first planetesimals, some of which underwent differentiation very early on. The isotopic signatures of volatiles were also fixed very early and may even have preceded the first episodes of condensation and accretion. Throughout the accretion of the Earth, volatile elements were delivered by material from both the inner (dry, volatile-poor) and outer (volatile-rich) solar system. This delivery was concomitant with the metals and silicates that form the bulk of the planet. The contribution of bodies that formed in the far outer solar system, a region now populated by comets, is likely to have been very limited. In that sense, volatile elements were contributed continuously throughout Earth’s accretion from inner solar system reservoirs, which also provided the silicates and metal building blocks of the inner planets. Following accretion, it likely took a few hundred million years for the Earth’s atmosphere and oceans to stabilise. Luckily, we have been able to access a compositional record of the early atmosphere and oceans through the analysis of palaeo-atmospheric fluids trapped in Archean hydrothermal quartz. From these analyses, it appears that the surface reservoirs of the Earth evolved due to interactions between the early Sun and the top of the atmosphere, as well as the development of an early biosphere that progressively altered its chemistry.

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Thi, W. F., S. Hocuk, I. Kamp, P. Woitke, Ch Rab, S. Cazaux et P. Caselli. « Warm dust surface chemistry ». Astronomy & ; Astrophysics 634 (février 2020) : A42. http://dx.doi.org/10.1051/0004-6361/201731746.

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Context. Molecular hydrogen (H2) is the main constituent of the gas in the planet-forming disks that surround many pre-main-sequence stars. H2 can be incorporated in the atmosphere of the nascent giant planets in disks. Deuterium hydride (HD) has been detected in a few disks and can be considered the most reliable tracer of H2, provided that its abundance throughout the disks with respect to H2 is well understood. Aims. We wish to form H2 and HD efficiently for the varied conditions encountered in protoplanetary disks: the densities vary from 104 to 1016 cm−3; the dust temperatures range from 5 to 1500 K, the gas temperatures go from 5 to a few 1000 Kelvin, and the ultraviolet radiation field can be 107 stronger than the standard interstellar field. Methods. We implemented a comprehensive model of H2 and HD formation on cold and warm grain surfaces and via hydrogenated polycyclic aromatic hydrocarbons in the physico-chemical code PROtoplanetary DIsk MOdel. The H2 and HD formation on dust grains can proceed via the Langmuir-Hinshelwood and Eley-Ridel mechanisms for physisorbed or chemisorbed H (D) atoms. H2 and HD also form by H (D) abstraction from hydrogenated neutral and ionised PAHs and via gas phase reactions. Results. H2 and HD are formed efficiently on dust grain surfaces from 10 to ~700 K. All the deuterium is converted into HD in UV shielded regions as soon as H2 is formed by gas-phase D abstraction reactions. The detailed model compares well with standard analytical prescriptions for H2 (HD) formation. At low temperature, H2 is formed from the encounter of two physisorbed atoms. HD molecules form on the grain surfaces and in the gas-phase. At temperatures greater than 20 K, the encounter between a weakly bound H- (or D-) atom or a gas-phase H (D) atom and a chemisorbed atom is the most efficient H2 formation route. H2 formation through hydrogenated PAHs alone is efficient above 80 K. However, the contribution of hydrogenated PAHs to the overall H2 and HD formation is relatively low if chemisorption on silicate is taken into account and if a small hydrogen abstraction cross-section is used. The H2 and HD warm grain surface network is a first step in the construction of a network of high-temperature surface reactions.

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Owen, James E. « Atmospheric Escape and the Evolution of Close-In Exoplanets ». Annual Review of Earth and Planetary Sciences 47, n^o 1 (30 mai 2019) : 67–90. http://dx.doi.org/10.1146/annurev-earth-053018-060246.

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Exoplanets with substantial hydrogen/helium atmospheres have been discovered in abundance, many residing extremely close to their parent stars. The extreme irradiation levels that these atmospheres experience cause them to undergo hydrodynamic atmospheric escape. Ongoing atmospheric escape has been observed to be occurring in a few nearby exoplanet systems through transit spectroscopy both for hot Jupiters and for lower-mass super-Earths and mini-Neptunes. Detailed hydrodynamic calculations that incorporate radiative transfer and ionization chemistry are now common in one-dimensional models, and multidimensional calculations that incorporate magnetic fields and interactions with the interstellar environment are cutting edge. However, comparison between simulations and observations remains very limited. While hot Jupiters experience atmospheric escape, the mass-loss rates are not high enough to affect their evolution. However, for lower-mass planets, atmospheric escape drives and controls their evolution, sculpting the exoplanet population that we observe today. ▪ Observations of some exoplanets have detected atmospheric escape driven by hydrodynamic outflows, causing the exoplanets to lose mass over time. ▪ Hydrodynamic simulations of atmospheric escape are approaching the sophistication required to compare them directly to observations. ▪ Atmospheric escape sculpts sharp features into the exoplanet population that we can observe today; these features have recently been detected.

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Fárník, Michal, Juraj Fedor, Jaroslav Kočišek, Jozef Lengyel, Eva Pluhařová, Viktoriya Poterya et Andriy Pysanenko. « Pickup and reactions of molecules on clusters relevant for atmospheric and interstellar processes ». Physical Chemistry Chemical Physics 23, n^o 5 (2021) : 3195–213. http://dx.doi.org/10.1039/d0cp06127a.

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Sreejith, A. G., L. Fossati, A. Youngblood, K. France et S. Ambily. « Ca II H&K stellar activity parameter : a proxy for extreme ultraviolet stellar fluxes ». Astronomy & ; Astrophysics 644 (décembre 2020) : A67. http://dx.doi.org/10.1051/0004-6361/202039167.

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Atmospheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. Atmospheric escape from giant planets is driven primarily by the stellar X-ray and extreme ultraviolet (EUV) radiation. Furthermore, EUV and longer wavelength UV radiation power disequilibrium chemistry in the middle and upper atmospheres. Our understanding of atmospheric escape and chemistry, therefore, depends on our knowledge of the stellar UV fluxes. While the far-ultraviolet (FUV) fluxes can be observed for some stars, most of the EUV range is unobservable due to the lack of a space telescope with EUV capabilities and, for the more distant stars, due to interstellar medium absorption. Therefore, it becomes essential to have an indirect means for inferring EUV fluxes from features observable at other wavelengths. We present here analytic functions for predicting the EUV emission of F-, G-, K-, and M-type stars from the log R′HK activity parameter that is commonly obtained from ground-based optical observations of the Ca II H&K lines. The scaling relations are based on a collection of about 100 nearby stars with published log R′HK and EUV flux values, the latter of which are either direct measurements or inferences from high-quality FUV spectra. The scaling relations presented here return EUV flux values with an accuracy of about a factor of three, which is slightly lower than that of other similar methods based on FUV or X-ray measurements.

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Mann, Ingrid, Pavel Spurný, Jack Baggaley, Jiří Borovička, Pavel Spurný, J. Watanabe, I. P. Williams, Vladimír Porubčan, Peter Jeniskens et Monica Grady. « Commission 22 : Meteors, Meteorites & ; Interplanetary Dust ». Proceedings of the International Astronomical Union 1, T26A (décembre 2005) : 167–70. http://dx.doi.org/10.1017/s1743921306004455.

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There have been three international meetings where the subject area of the meeting was to significant extent within the area of interest of commission 22. These were: The Meteoroids 2004 Conference was held at the University of Western Ontario in London, Canada from August 15 to 21, 2004. This conference was the fifth in a series of meteoroid meetings which have been held approximately every three years since 1992, the previous one being in Kiruna, Sweden in 2001. Ingrid Mann chaired a scientific organizing committee which set the program for the conference. The meeting brought together scientists from more than twenty countries, to deliver 84 oral and 38 poster presentations. The papers represented the research contributions of more than 150 different scientists. The conference provided a comprehensive overview of leading edge research on topics ranging from the dynamics, sources and distribution of meteoroids, their chemistry and their physical processes in the interplanetary medium and the Earthõs atmosphere, and space and laboratory studies of meteorites, micrometeorites and interplanetary dust were also well represented. It was clear from the conference that the coordinated international campaigns for the Leonid showers provided a rich observational dataset and lead to the development of new observational and analysis techniques. Another trend obvious at the conference was the increasing use of sophisticated large aperture radars for meteor studies. High performance computing facilitates both dynamical model calculations and sophisticated ablation models. Significant progress was reported on ablation models for meteoroids ranging from dust to those producing bright fireballs. Study of solid particles entering the solar system from interstellar space and improved dust measuring capabilities on interplanetary spacecraft are an important research area which links astrophysical dust with solar system dust. The majority of papers presented at the conference (a total of 69 papers) are being published as a special issue of the journal Earth, Moon, and Planets (Vol. 95, Nos. 1–4) and also in the form of an associated book published by Springer: Modern Meteor Science: An Interdisciplinary View which was edited by R.Hawkes, I. Mann and P. Brown (ISBN 1-4020-4374-0). The book will be accompanied by a CD-ROM which includes a selection of conference photographs and the complete abstracts of all papers from the conference. As is reflected in the title of the spin-off book, this field is becoming increasingly interdisciplinary in nature, with researchers from astronomy, astrophysics, space science, space engineering, cosmochemistry, atmospheric science and geophysics, as well as others, now contributing to research in the field.

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Vastel, C., J. C. Loison, V. Wakelam et B. Lefloch. « Isocyanogen formation in the cold interstellar medium ». Astronomy & ; Astrophysics 625 (mai 2019) : A91. http://dx.doi.org/10.1051/0004-6361/201935010.

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Context. Cyanogen (NCCN) is the simplest member of the dicyanopolyynes group, and has been proposed as a major source of the CN radical observed in cometary atmospheres. Although not detected through its rotational spectrum in the cold interstellar medium, this very stable species is supposed to be very abundant. Aims. The chemistry of cyanogen in the cold interstellar medium can be investigated through its metastable isomer, CNCN (isocyanogen). Its formation may provide a clue on the widely abundant CN radical observed in cometary atmospheres. Methods. We performed an unbiased spectral survey of the L1544 proto-typical prestellar core, using the IRAM-30 m and have analysed, for this paper, the nitrogen chemistry that leads to the formation of isocyanogen. We report on the first detection of CNCN, NCCNH+, C3N, CH3CN, C2H3CN, and H2CN in L1544. We built a detailed chemical network for NCCN/CNCN/HC2N2+ involving all the nitrogen bearing species detected (CN, HCN, HNC, C3N, CNCN, CH3CN, CH2CN, HCCNC, HC3N, HNC3, H2CN, C2H3CN, HCNH+, HC3NH+) and the upper limits on C4N, C2N. The main cyanogen production pathways considered in the network are the CN + HNC and N + C3N reactions. Results. The comparison between the observations of the nitrogen bearing species and the predictions from the chemical modelling shows a very good agreement, taking into account the new chemical network. The expected cyanogen abundance is greater than the isocyanogen abundance by a factor of 100. Although cyanogen cannot be detected through its rotational spectrum, the chemical modelling predicts that it should be abundant in the gas phase and hence might be traced through the detection of isocyanogen. It is however expected to have a very low abundance on the grain surfaces compared to HCN.

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Moore, Peter W., Jordan P. Hooker, Athanasios Zavras, George N. Khairallah, Elizabeth H. Krenske, Paul V. Bernhardt, Gina Quach, Evan G. Moore, Richard A. J. O'Hair et Craig M. Williams. « Hydroxyl Radicals via Collision-Induced Dissociation of Trimethylammonium Benzyl Alcohols ». Australian Journal of Chemistry 70, n^o 4 (2017) : 397. http://dx.doi.org/10.1071/ch16602.

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The hydroxyl radical is a well known reactive oxygen species important for interstellar, atmospheric, and combustion chemistry in addition to multiple biochemical processes. Although there are many methods to generate the hydroxyl radical, most of these are inorganic based, with only a few originating from organic precursor molecules. Reported herein is the observation that trimethylammonium benzyl alcohols and their corresponding deuterated isotopologues act as a good source of hydroxyl and deuteroxyl radicals in the gas-phase under collision-induced dissociation (CID) conditions. Attempts to replicate this chemistry in the condensed phase are described.

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Falgarone, Edith, Benjamin Godard et Pierre Hily-Blant. « Turbulence in the Diffuse Interstellar Medium ». Proceedings of the International Astronomical Union 7, S280 (juin 2011) : 187–202. http://dx.doi.org/10.1017/s1743921311024975.

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AbstractThe diffuse interstellar medium (ISM) hosts the first steps of interstellar chemistry and the seeds of dense structures. Since its turbulent pressure by far exceeds its thermal pressure, turbulence must play a prominent role in its evolution. Fed at galactic scales, turbulent energy cascades down to the dissipation scales, but as in both laboratory and atmospheric turbulence, it does so in an intermittent way : only a tiny fraction of the small-scales is fed by the turbulent cascade, so that dissipation occurs in bursts. In diffuse molecular clouds, where they can be observed, the signatures of intermittency are: (1) the non-Gaussian statistics of velocity increments, and (2) the existence of coherent structures of intense velocity-shear that appear to channel the large-scale turbulent energy down to milliparsec scales. Attempts at modelling the warm chemistry triggered in the diffuse ISM by bursts of turbulent dissipation are promising : in this framework, the so far unexplained molecular richness observed in this medium is naturally understood, in particular its CH+, HCO+ and CO abundances. Turbulent dissipation is also likely at the origin of the H2 rotational line emission of the diffuse ISM and of a significant fraction of its [C II] emission.

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Puzzarini, Cristina. « Prebiotic molecules in interstellar space : Rotational spectroscopy and quantum chemistry ». Proceedings of the International Astronomical Union 15, S350 (avril 2019) : 65–70. http://dx.doi.org/10.1017/s1743921319007592.

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AbstractThe starting point for the development of any astrochemical model is the knowledge of whether a molecule is present in the astrophysical environment considered, with the astronomical observations of spectroscopic signatures providing the unequivocal proof of its presence. Among the goals of astrochemistry, the detection of potential prebiotic molecules in the interstellar medium and planetary atmospheres is fundamental in view of possibly understanding the origin of life. The detection of new molecules in space requires the spectroscopic signatures (mostly, rotational transition frequencies) to be accurately determined over a large frequency range. This task is more and more often the result of a synergic interplay of experiment and theory.

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Linsky, Jeffrey L., Kevin France et Tom Ayres. « Reconstructing the Stellar UV and EUV Emission that Controls the Chemistry of Exoplanet Atmospheres ». Proceedings of the International Astronomical Union 8, S293 (août 2012) : 309–14. http://dx.doi.org/10.1017/s1743921313013057.

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AbstractLyman-α and extreme-ultraviolet radiation from exoplanet host stars are critically important for evaluating the phototchemistry of planetary atmospheres, but these emissions are largely or completely absorbed by hydrogen in the interstellar medium. We describe a new technique for estimating the intrinsic Lyman-α and EUV fluxes of F, G, K, and M stars using correlations with observable emission lines.

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Satta, Mauro, Mattea Carmen Castrovilli, Francesca Nicolanti, Anna Rita Casavola, Carlo Mancini Terracciano et Antonella Cartoni. « Perspectives of Gas Phase Ion Chemistry : Spectroscopy and Modeling ». Condensed Matter 7, n^o 3 (21 juillet 2022) : 46. http://dx.doi.org/10.3390/condmat7030046.

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The study of ions in the gas phase has a long history and has involved both chemists and physicists. The interplay of their competences with the use of very sophisticated commercial and/or homemade instrumentations and theoretical models has improved the knowledge of thermodynamics and kinetics of many chemical reactions, even if still many stages of these processes need to be fully understood. The new technologies and the novel free-electron laser facilities based on plasma acceleration open new opportunities to investigate the chemical reactions in some unrevealed fundamental aspects. The synchrotron light source can be put beside the FELs, and by mass spectrometric techniques and spectroscopies coupled with versatile ion sources it is possible to really change the state of the art of the ion chemistry in different areas such as atmospheric and astro chemistry, plasma chemistry, biophysics, and interstellar medium (ISM). In this manuscript we review the works performed by a joint combination of the experimental studies of ion–molecule reactions with synchrotron radiation and theoretical models adapted and developed to the experimental evidence. The review concludes with the perspectives of ion–molecule reactions by using FEL instrumentations as well as pump probe measurements and the initial attempt in the development of more realistic theoretical models for the prospective improvement of our predictive capability.

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SMITH, R. SCOTT, et BRUCE D. KAY. « MOLECULAR BEAM STUDIES OF KINETIC PROCESSES IN NANOSCALE WATER FILMS ». Surface Review and Letters 04, n^o 04 (août 1997) : 781–97. http://dx.doi.org/10.1142/s0218625x97000766.

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Studies of the properties of crystalline ice and amorphous solid water are the focus of considerable diverse and interdisciplinary research. The reasons include understanding heterogeneous atmospheric processes, interstellar and cometary astrophysics, cryobiology, and the physics and chemistry of liquids. In this review we summarize our recent work using nanoscale ice films to characterize the kinetic behavior of crystalline ice and amorphous solid water. The adsorption, desorption, crystallization and diffusion kinetics of the nanoscale films are studies using molecular beam and programmed desorption techniques. The results of these experiments and their implications for the physical properties of nanoscale ice films are presented.

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Balucani, Nadia. « Gas-phase prebiotic chemistry in extraterrestrial environments ». Proceedings of the International Astronomical Union 5, H15 (novembre 2009) : 682–83. http://dx.doi.org/10.1017/s1743921310010938.

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AbstractA variety of molecular species up to complex polyatomic molecules/radicals have been identified in many extraterrestrial gaseous environments, including interstellar clouds, cometary comae and planetary atmospheres. Amongst the identified molecules/radicals, a large percentage are organic in nature and encompass also prebiotic molecules. Different types of microscopic processes are believed to be involved in their formation, including surface processes, ion- and radical- molecule reactions. A thorough characterization of such a complex chemistry relies on a multi-disciplinary approach, where the observations are complemented by accurate chemical modeling. Unfortunately, a literature survey reveals that only a small percentage of the elementary reactions considered in the available models have been characterized in laboratory experiments. In this contribution, a brief overview will be given of recent experimental techniques that have allowed us to reach a better description of neutral-neutral gas-phase reactions, which might be responsible for the formation of simple prebiotic molecules.

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Srećković, Vladimir A., Darko Jevremović, Veljko Vujčić, Ljubinko M. Ignjatović, Nenad Milovanović, Sanja Erkapić et Milan S. Dimitrijević. « Mol-D a Database and a Web Service within the Serbian Virtual Observatory and the Virtual Atomic and Molecular Data Centre ». Proceedings of the International Astronomical Union 12, S325 (octobre 2016) : 393–96. http://dx.doi.org/10.1017/s1743921316012643.

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AbstractIn this contribution we report the current stage of the MOLecular Dissociation (MOL-D) database which is a web service within the Serbian virtual observatory (SerVO) and node within Virtual Atomic and Molecular Data Center (VAMDC). MOL-D is an atomic and molecular (A&M) database devoted to the modelling of stellar atmospheres, laboratory plasmas, industrial plasmas etc. The initial stage of development was done at the end of 2014, when the service for data connected with hydrogen and helium molecular ions was done. In the next stage of the development of MOL-D, we include new cross-sections and rate coefficients for processes which involve species such as XH+, where X is atom of some metal. Data are important for the exploring of the interstellar medium as well as for the early Universe chemistry and for the modeling of stellar and solar atmospheres. In this poster, we present our ongoing work and plans for the future.

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Stoicheff, Boris P. « Gerhard Herzberg PC CC. 25 December 1904 – 3 March 1999 ». Biographical Memoirs of Fellows of the Royal Society 49 (janvier 2003) : 179–95. http://dx.doi.org/10.1098/rsbm.2003.0011.

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Gerhard Herzberg, Nobel Laureate in Chemistry, had broad interests and achieved supreme accomplishments in physics, chemistry and astrophysics. The high points in his research were many. In physics they were the work on atomic hydrogen and helium, and evaluations of energy levels and constants of molecular hydrogen and its isotopes. His determinations of many molecular structures and discoveries of spectra of the free radicals CH 2 and CH 3 , and of the Rydberg molecule H3, were each outstanding contributions in chemistry. In astrophysics, his reproduction in the laboratory of the spectrum of CH + , proving its presence in the interstellar medium, and of spectra of C 3 and H 2 O + and their presence in comets, his observation of the quadrupole spectrum of H 2 and his discovery of hydrogen in the atmospheres of the planets opened up new applications of spectroscopy for our knowledge of the universe. His classic volumes on molecular spectra and molecular structures remain as encyclopaedias of molecular knowledge for all time. And his famous laboratory, the ‘Temple of spectroscopy’, served as a home for hundreds of scientists around the world, and helped to bring Canadian science to international prominence.

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Hartquist, Thomas W., et Ewine F. Van Dishoeck. « Alexander Dalgarno. 5 January 1928—9 April 2015 ». Biographical Memoirs of Fellows of the Royal Society 69 (5 août 2020) : 145–74. http://dx.doi.org/10.1098/rsbm.2020.0009.

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Alexander (Alex) Dalgarno greatly advanced the quantitative study of fundamental atomic and molecular processes, contributed significantly to atmospheric science and ‘established molecular astrophysics as a unified intellectual field of great scientific endeavour, impact and achievement’ ( Flannery 2010 ). Alex developed and applied techniques that simplify calculations and lead to reliable solutions, enabling him to make landmark contributions to the knowledge of collisionally induced charge transfer, rotational and vibrational excitation of molecules, spin exchange and ultracold chemistry. His wide-ranging curiosity, disciplined steps to broaden his programme and ability to identify dominant physical processes and calculate their rates led to his many important contributions to atmospheric science. For example, Alex greatly expanded the knowledge of terrestrial airglow features, photoabsorption and collisional processes in the terrestrial ozone layer and deposition by energetic electrons in the atmospheres of other planets. In molecular astrophysics, he applied that same systematic approach to studies of a range of environments from the early Universe to present-day UV-irradiated interstellar clouds, shocks and supernova ejecta. Alex made availability to students a priority and encouraged them to pursue problems that they devised, despite his seemingly inexhaustible supply of suitable projects. His community service included his 29-year long editorship of Astrophysical Journal Letters , starting in 1973, and the founding of the Institute of Theoretical Atomic and Molecular Physics at the Harvard-Smithsonian Center for Astrophysics, in 1988, owing to his concerns for the health of the fields of theoretical atomic and molecular physics and fundamental quantum mechanics, which the Institute did much to reinvigorate.

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Wu, Junjun, Hongbo Ning, Liuhao Ma et Wei Ren. « Pressure-dependent kinetics of methyl formate reactions with OH at combustion, atmospheric and interstellar temperatures ». Physical Chemistry Chemical Physics 20, n^o 41 (2018) : 26190–99. http://dx.doi.org/10.1039/c8cp04114h.

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Jacovella, Ugo, Giel Muller, Katherine J. Catani, Nastasia I. Bartlett et Evan J. Bieske. « Electronic Spectra of the Triacetylene Cation (HC6H+) and Protonated Triacetylene (HC6H2+) Tagged with Ar ». Australian Journal of Chemistry 72, n^o 4 (2019) : 260. http://dx.doi.org/10.1071/ch18508.

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Polyacetylene cations (HC2nH+) play important roles in combustion processes and in the chemistry of planetary atmospheres and interstellar clouds. Here we report the electronic spectrum for the triacetylene cation (HC6H+) recorded over the 300–610nm range by photodissociating mass-selected ions tagged with argon atoms in a tandem mass spectrometer. The spectrum shows three band systems that are assigned to (origin transition 16665cm−1), (origin transition 23916cm−1), and (origin transition 29920cm−1). Although the band system is well known, the and band systems are observed for the first time in the gas phase. In addition, the electronic spectrum of the protonated triacteylene cation tagged with an argon atom (HC6-Ar) is reported, providing the first gas-phase spectrum for this species.

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Pontoppidan, Klaus M. « Observations of planet-forming volatiles ». Proceedings of the International Astronomical Union 11, A29B (août 2015) : 390–94. http://dx.doi.org/10.1017/s1743921316005615.

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AbstractWater is observed to be a major constituent of planet-forming disks around young stars and its presence likely plays a major role in formation of planets and their atmospheres, including those destined to orbit in a habitable zone. Yet, the path from disks to planets is one fraught with complexity, making it difficult to derive precise theoretical predictions for planetary chemistry. Planet-forming disks are no longer considered uniform well-mixed structures; rather, they are complex worlds with many different heterogenous environments, most of which play some part in determining the composition of planetesimals and planets. Direct observations of atomic and molecular abundances on all size scales are therefore needed for understanding planet formation at a very fundamental level, and for answering the question of how chemically common the Earth is among exoplanets. In the past years, great progress has been made in observing protoplanetary chemistry, in particular in measuring the molecular composition in protoplanetary disks across the planet-forming regions from 1 to 10s of AU. We will present recent observations of water with Herschel, the VLT and Gemini in disks, and we will demonstrate how we retrieve the local abundances and radial distribution of water vapor and ice using detailed radiative transfer models. We find that most of the oxygen is likely bound in water near 1 AU in disks around solar-mass stars and that the disk surface composition at these radii is likely dominated by local gas-phase chemistry rather than by primordial material delivered from the interstellar medium. We discuss how these observations relate to complementary constraints from the solar system. We further discuss the implications for the observed composition of exoplanetary atmospheres.

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Velilla-Prieto, L., J. Cernicharo, M. Agúndez, J. P. Fonfría, A. Castro-Carrizo, G. Quintana-Lacaci, N. Marcelino et al. « Circumstellar chemistry of Si-C bearing molecules in the C-rich AGB star IRC+10216 ». Proceedings of the International Astronomical Union 14, S343 (août 2018) : 535–37. http://dx.doi.org/10.1017/s1743921318005410.

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AbstractSilicon carbide together with amorphous carbon are the main components of dust grains in the atmospheres of C-rich AGB stars. Small gaseous Si-C bearing molecules (such as SiC, SiCSi, and SiC2) are efficiently formed close to the stellar photosphere. They likely condense onto dust seeds owing to their highly refractory nature at the lower temperatures (i.e., below about 2500 K) in the dust growth zone which extends a few stellar radii from the photosphere. Beyond this region, the abundances of Si-C bearing molecules are expected to decrease until they are eventually reformed in the outer shells of the circumstellar envelope, owing to the interaction between the gas and the interstellar UV radiation field. Our goal is to understand the time-dependent chemical evolution of Si-C bond carriers probed by molecular spectral line emission in the circumstellar envelope of IRC+10216 at millimeter wavelengths.

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Coyne, John P., et David W. Ball. « Alpha particle chemistry. On the formation of stable complexes between He2+ and other simple species : implications for atmospheric and interstellar chemistry ». Journal of Molecular Modeling 15, n^o 1 (21 octobre 2008) : 35–40. http://dx.doi.org/10.1007/s00894-008-0371-3.

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Redondo, P., F. Pauzat, Y. Ellinger et A. Markovits. « Reconstruction of water ice : the neglected process OH + OH → H2O + O ». Astronomy & ; Astrophysics 638 (juin 2020) : A125. http://dx.doi.org/10.1051/0004-6361/202037771.

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Context. Although H2O is the most important molecular material found in the solid state in the interstellar medium, the chemical routes leading to ice through surface reactions are still a matter of discussion. Three reaction pathways proposed in the past are at the heart of current research: hydrogenation of atomic oxygen, molecular oxygen, and ozone. The reaction network finally leads to a small number of processes giving H2O: H + OH, H2 + OH, and H + H2O2. To these processes, OH + OH should be added. It is known to be efficient in atmospheric chemistry and takes the irradiations of the interstellar grains into account that, directly or indirectly, create a number of OH radicals on and in the icy mantles. Aims. We study the role of the existing ice in its own reconstruction after it is destroyed by the constant irradiation of interstellar grains and focus on the OH + OH reaction in the triplet state. Methods. We used numerical simulations with a high level of coupled cluster ab initio calculations for small water aggregates and methods relevant to density functional theory for extended systems, including a periodic description in the case of solid water of infinite dimensions. Results. OH + OH → H2O + O reaction profiles are reported that take the involvement of an increasing number of H2O support molecules into account. It is found that the top of the barrier opposing the reaction gradually decreases with the number of supporting H2O and falls below the level of the reactants for H2O layers or solid water. Conclusions. In contrast to the gas phase, the reaction is barrierless on water ice. By adding a reconstructed H2O molecule and a free oxygen atom at the surface of the remaining ice, this reaction leaves open the possibility of the ice reconstruction.

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Gao, Lu Gem, Jingjing Zheng, Antonio Fernández-Ramos, Donald G. Truhlar et Xuefei Xu. « Kinetics of the Methanol Reaction with OH at Interstellar, Atmospheric, and Combustion Temperatures ». Journal of the American Chemical Society 140, n^o 8 (19 février 2018) : 2906–18. http://dx.doi.org/10.1021/jacs.7b12773.

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Anicich, V. G., et W. T. ,. Jr Huntress. « A survey of bimolecular ion-molecule reactions for use in modeling the chemistry of planetary atmospheres, cometary comae, and interstellar clouds ». Astrophysical Journal Supplement Series 62 (novembre 1986) : 553. http://dx.doi.org/10.1086/191151.

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Bovino, S., S. Ferrada-Chamorro, A. Lupi, D. R. G. Schleicher et P. Caselli. « A new proxy to estimate the cosmic ray ionization rate in dense cores ». Monthly Notices of the Royal Astronomical Society : Letters 495, n^o 1 (19 mars 2020) : L7—L11. http://dx.doi.org/10.1093/mnrasl/slaa048.

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ABSTRACT Cosmic rays are a global source of ionization, and the ionization fraction represents a fundamental parameter in the interstellar medium. Ions couple to magnetic fields, and affect the chemistry and the dynamics of star-forming regions as well as planetary atmospheres. However, the cosmic ray ionization rate represents one of the bottlenecks for astrochemical models, and its determination is one of the most puzzling problems in astrophysics. While for diffuse clouds reasonable values have been provided from ${\mathrm{ H}_3}^+$ observations, for dense clouds, due to the lack of rotational transitions, this is not possible, and estimates are strongly biased by the employed model. We present here an analytical expression, obtained from first principles, to estimate the cosmic ray ionization rate from observational quantities. The theoretical predictions are validated with high-resolution 3D numerical simulations and applied to the well-known core L1544; we obtained an estimate of ζ2 ∼ 2–3 × 10−17 s−1. Our results and the analytical formulae provided represent the first model-independent robust tool to probe the cosmic ray ionization rate in the densest part of star-forming regions (on spatial scales of R ≤ 0.05 pc). An error analysis is presented to give statistical relevance to our study.

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Anicich, V. G. « A survey of bimolecular ion-molecule reactions for use in modeling the chemistry of planetary atmospheres, cometary comae, and interstellar clouds - 1993 supplement ». Astrophysical Journal Supplement Series 84 (février 1993) : 215. http://dx.doi.org/10.1086/191752.

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Picaud, Sylvain, et Pál Jedlovszky. « Molecular-scale simulations of organic compounds on ice : application to atmospheric and interstellar sciences ». Molecular Simulation 45, n^o 4-5 (6 août 2018) : 403–16. http://dx.doi.org/10.1080/08927022.2018.1502428.

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Perrero, Jessica, Joan Enrique-Romero, Berta Martínez-Bachs, Cecilia Ceccarelli, Nadia Balucani, Piero Ugliengo et Albert Rimola. « Non-energetic Formation of Ethanol via CCH Reaction with Interstellar H₂O Ices. A Computational Chemistry Study ». ACS Earth and Space Chemistry 6, n^o 3 (7 mars 2022) : 496–511. http://dx.doi.org/10.1021/acsearthspacechem.1c00369.

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Maté, Belén, Stéphanie Cazaux, Miguel Ángel Satorre, Germán Molpeceres, Juan Ortigoso, Carlos Millán et Carmina Santonja. « Diffusion of CH4 in amorphous solid water ». Astronomy & ; Astrophysics 643 (novembre 2020) : A163. http://dx.doi.org/10.1051/0004-6361/202038705.

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Context. The diffusion of volatile species on amorphous solid water ice affects the chemistry on dust grains in the interstellar medium as well as the trapping of gases enriching planetary atmospheres or present in cometary material. Aims. The aim of the work is to provide diffusion coefficients of CH4 on amorphous solid water (ASW) and to understand how they are affected by the ASW structure. Methods. Ice mixtures of H2O and CH4 were grown in different conditions and the sublimation of CH4 was monitored via infrared spectroscopy or via the mass loss of a cryogenic quartz crystal microbalance. Diffusion coefficients were obtained from the experimental data assuming the systems obey Fick’s law of diffusion. Monte Carlo simulations were used to model the different amorphous solid water ice structures investigated and were used to reproduce and interpret the experimental results. Results. Diffusion coefficients of methane on amorphous solid water have been measured to be between 10−12 and 10−13 cm2 s−1 for temperatures ranging between 42 K and 60 K. We show that diffusion can differ by one order of magnitude depending on the morphology of amorphous solid water. The porosity within water ice and the network created by pore coalescence enhance the diffusion of species within the pores. The diffusion rates derived experimentally cannot be used in our Monte Carlo simulations to reproduce the measurements. Conclusions. We conclude that Fick’s laws can be used to describe diffusion at the macroscopic scale, while Monte Carlo simulations describe the microscopic scale where trapping of species in the ices (and their movement) is considered.

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de Souza Machado, Gladson, Eduardo Monteiro Martins, Leonardo Baptista et Glauco F. Bauerfeldt. « Prediction of Rate Coefficients for the H2CO + OH → HCO + H2O Reaction at Combustion, Atmospheric and Interstellar Medium Conditions ». Journal of Physical Chemistry A 124, n^o 11 (24 février 2020) : 2309–17. http://dx.doi.org/10.1021/acs.jpca.9b11690.

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da Silva, Gabriel. « Reaction of Benzene with Atomic Carbon : Pathways to Fulvenallene and the Fulvenallenyl Radical in Extraterrestrial Atmospheres and the Interstellar Medium ». Journal of Physical Chemistry A 118, n^o 22 (27 mai 2014) : 3967–72. http://dx.doi.org/10.1021/jp503431a.

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Field, D., J. P. Simons et Charles Cockell. « Sydney Leach. 11 April 1924—24 December 2019 ». Biographical Memoirs of Fellows of the Royal Society 69 (16 septembre 2020) : 313–32. http://dx.doi.org/10.1098/rsbm.2020.0018.

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Sydney Leach will be remembered as an outstanding and inspirational scientist, an irreplaceable friend to many—artists and musicians as well as academic colleagues. He encouraged and influenced numerous scientists as a mentor. After graduating from King's College London and carrying out war work at Farnborough, he spent all his scientific life based in Paris, working principally at Orsay and, in his later years, at the Observatoire de Paris–Meudon. Sydney was a major influence in establishing chemical physics in France after World War II, founding the highly influential Laboratoire de Photophysique Moléculaire (LPPM) at Orsay, where much of his pioneering work was performed. The ‘Sydney lab’ lives on in the newly created Institut des Sciences Moléculaires d'Orsay. Early experiments often took place at the synchrotron source (ACO, Super-ACO), just a few hundred yards from LPPM. He was a pioneering advocate of synchrotron radiation, and a driving force for its use in spectroscopy and photodynamics, along with free-electron lasers, supersonic jets, coincidence spectroscopy and matrix isolation—techniques that were applied and refined over decades and used to explore fundamental processes such as photoionization, vibronic coupling and radiationless transitions. Sydney's seminal studies of polyatomic molecular ions led him towards fresh horizons in planetary atmospheric and space science. His work opened new vistas in cometary spectroscopy, polycyclic aromatic hydrocarbons, fullerenes and their possible roles in the chemistry of the interstellar medium and, finally, biologically relevant species, helping to instigate the newly developing subject of astrobiology—a perfect example of his sustained prescience in the world of science.

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Origlia, L., E. Dalessandro, N. Sanna, A. Mucciarelli, E. Oliva, G. Cescutti, M. Rainer, A. Bragaglia et G. Bono. « Stellar population astrophysics (SPA) with the TNG ». Astronomy & ; Astrophysics 629 (septembre 2019) : A117. http://dx.doi.org/10.1051/0004-6361/201936283.

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Aims. The Scutum complex in the inner disk of the Galaxy hosts a number of young clusters and associations of red supergiant stars that are heavily obscured by dust extinction. These stars are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. Methods. Within the SPA Large Programme at the TNG, we secured GIANO-B high-resolution (R ≃ 50 000) YJHK spectra of 11 red supergiants toward the Alicante 7 and Alicante 10 associations near the RSGC3 cluster. Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to measure several hundreds of atomic and molecular lines that are suitable for chemical abundance determinations. We also measured a prominent diffuse interstellar band at λ1317.8 nm (vacuum). This provides an independent reddening estimate. Results. The radial velocities, Gaia proper motions, and extinction of seven red supergiants in Alicante 7 and three in Alicante 10 are consistent with them being members of the associations. One star toward Alicante 10 has kinematics and low extinction that are inconsistent with a membership. By means of spectral synthesis and line equivalent width measurements, we obtained chemical abundances for iron-peak, CNO, alpha, other light, and a few neutron-capture elements. We found average slightly subsolar iron abundances and solar-scaled [X/Fe] abundance patterns for most of the elements, consistent with a thin-disk chemistry. We found depletion of [C/Fe], enhancement of [N/Fe], and relatively low 12C/13C < 15, which is consistent with CN cycled material and possibly some additional mixing in their atmospheres.

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Namekata, Kosuke, Shin Toriumi, Vladimir S. Airapetian, Munehito Shoda, Kyoko Watanabe et Yuta Notsu. « Reconstructing the XUV Spectra of Active Sun-like Stars Using Solar Scaling Relations with Magnetic Flux ». Astrophysical Journal 945, n^o 2 (1 mars 2023) : 147. http://dx.doi.org/10.3847/1538-4357/acbe38.

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Abstract The Kepler space telescope and Transiting Exoplanet Survey Satellite unveiled that Sun-like stars frequently host exoplanets. These exoplanets are subject to fluxes of ionizing radiation in the form of X-ray and extreme-ultraviolet (EUV) radiation that may cause changes in their atmospheric dynamics and chemistry. While X-ray fluxes can be observed directly, EUV fluxes cannot be observed because of severe interstellar medium absorption. Here we present a new empirical method to estimate the whole stellar X-ray plus EUV (XUV) and far-UV (FUV) spectra as a function of total unsigned magnetic fluxes of stars. The response of the solar XUV and FUV spectrum (0.1–180 nm) to the solar total unsigned magnetic flux is investigated by using the long-term Sun-as-a-star data set over 10 yr, and the power-law relation is obtained for each wavelength with a spectral resolution of 0.1–1 nm. We applied the scaling relations to active young Sun-like stars (G dwarfs), EK Dra (G1.5V), π 1 Uma (G1.5V), and κ 1 Ceti (G5V) and found that the observed spectra (except for the unobservable longward EUV wavelength) are roughly consistent with the extension of the derived power-law relations with errors of an order of magnitude. This suggests that our model is a valuable method to derive the XUV/FUV fluxes of Sun-like stars, including the EUV band mostly absorbed at wavelengths longward of 36 nm. We also discuss differences between the solar extensions and stellar observations at wavelengths in the 2–30 nm band and conclude that simultaneous observations of magnetic and XUV/FUV fluxes are necessary for further validations.

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Thiem, T. L. « Spectroscopy of the Earth′s Atmosphere and Intersteller Medium. Edited by N. Narahari Rao and Alfons Weber. Academic Press, San Diego, CA, 1992. 518 pp. + index, $129.50. » Microchemical Journal 50, n^o 1 (août 1994) : 125. http://dx.doi.org/10.1006/mchj.1994.1068.

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Koppenol, W. H. « Names for inorganic radicals (IUPAC Recommendations 2000) ». Pure and Applied Chemistry 72, n^o 3 (1 janvier 2000) : 437–46. http://dx.doi.org/10.1351/pac200072030437.

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Introduction: Knowledge of the properties and reactivities of stable inorganic radicals was obtained decades ago through gas-phase studies of various oxides of halogens, sulfur, and nitrogen. More recently, pulse radiolysis and flash photolysis techniques developed in the 1960s made it possible to study short-lived radicals, such as hydrated electrons, hydrogen atoms, and hydroxyl radicals. Because of the high time-resolution of these techniques, absorption spectra and redox properties of these inorganic radicals could be determined. The interest in radicals increased when it was shown that superoxide, or dioxide(1-), is formed in vivo. The discovery that in aerobic organisms enzymes catalyze the disproportionation of this radical resulted in new areas of research, such as radical biology and radicals in medicine. Interest in simple radicals was further boosted most recently by the remarkable observation that the radical nitrogen monoxide is formed enzymatically from the amino acid arginine. Radicals are important in a variety of catalytic processes and in the atmospheric gas and liquid phases; furthermore, a substantial number of inorganic radicals have been observed in interstellar gas clouds.Contents:1. Introduction 2. Definitions 3. Nomenclature 3.1. Introduction 3.2. Coordination nomenclature 3.2.1. Selection of the central atom3.2.2. Radicals with net charges 3.2.3. Attached atoms or groups of atoms 3.2.4. The radical dot 3.2.5. Examples 3.3. Substitutive nomenclature

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