Radiative decay rates for W I, W II and W III allowed and forbidden transitions of interest for spectroscopic diagnostics in fusion plasmas

Transition probabilities for allowed and forbidden lines in neutral, singly ionized and doubly ionized tungsten are discussed in the present paper. For the electric dipole transitions, recommended values are proposed from a critical evaluation of the data available in the literature. For the magnetic dipole and electric quadrupole transitions, for which no data have been published so far, a new set of radiative rates has been obtained using a relativistic Hartree–Fock approach including core-polarization effects. The tables summarizing the compiled data are expected to be useful for plasma modelling in fusion reactors

CHAPTER 14. New Directions for an Experimental Approach to the Chemistry of the Origin of Life

International audienc

Evolution of interstellar organic compounds under asteroidal hydrothermal conditions

International audienceCarbonaceous chondrites (CC) contain a diversity of organic compounds. No definitive evidence for a genetic relationship between these complex organic molecules and the simple organic molecules detected in the interstellar medium (ISM) has yet been reported. One of the many difficulties arises from the transformations of organic compounds during accretion and hydrothermal alteration on asteroids. Here, we report results of hydrothermal alteration experiments conducted on a common constituent of interstellar ice analogs, Hexamethylenetetramine (HMT – C 6 H 12 N 4). We submitted HMT to asteroidal hydrothermal conditions at 150 °C, for various durations (up to 31 days) and under alkaline pH. Organic products were characterized by gas chromatography mass spectrometry, infrared spectroscopy and synchrotron-based X-ray absorption near edge structure spectroscopy. Results show that, within a few days, HMT has evolved into (1) a very diverse suite of soluble compounds dominated by N-bearing aromatic compounds (> 150 species after 31 days), including for instance formamide, pyridine, pyrrole and their polymers (2) an aromatic and N-rich insoluble material that forms after only 7 days of experiment and then remains stable through time. The reaction pathways leading to the soluble compounds likely include HMT dissociation, formose and Maillard-type reactions, e.g. reactions of sugar derivatives with amines. The present study demonstrates that, if interstellar organic compounds such as HMT had been accreted by chondrite parent bodies, they would have undergone chemical transformations during hydrothermal alteration, potentially leading to the formation of high molecular weight insoluble organic molecules. Some of the diversity of soluble and insoluble organic compounds found in CC may thus result from asteroidal hydrothermal alteration

New insight into the formation of hexamethylenetetramine (HMT) in interstellar and cometary ice analogs

Aims. We investigate the purely thermal formation of hexamethylenetetramine (HMT, C6H12N4) in interstellar ice analogs from non-photolysed ice and compare our results with those for the formation from photolysed ice. Methods. We use Fourier transform-infrared spectroscopy to follow residue formation from VUV irradiation of H2CO:NH3 ice mixture in different concentration ratios. We also report the warming of the H2CO:NH3:HCOOH ice mixture. Results. We present the characterization of organic residues obtained at 330 K from VUV irradiation of H2CO:NH3 ice mixtures. The organic residues contain compounds related to polyoxomethylene (POM, [-CH2-O-]n) and HMT (C6H12N4). We report, for the first time, the formation of HMT from the warming of an interstellar ice analogs, H2CO:NH3:HCOOH, without any energetic processing (i.e. photons or particles). New insights into HMT formation mechanism are proposed. These results strengthen the hypothesis that HMT is present in interstellar grains or in comets, where it may be detected with the COSAC instrument of the Rosetta mission

Thermal Evolution of Interstellar Ice Analogues Containing Formaldehyde

WOS:000317632700055International audienceWe have developed a new laboratory approach to investigate the evolution of interstellar ices by separating thermal processing from VUV processing. Infrared spectroscopy and mass spectrometry are used to monitor the thermal evolution of ice containing formaldehyde (H2CO) and ammonia (NH3). The main idea is to distinguish photon-induced chemistry from thermally induced chemistry. We show that H2CO and NH3 thermally react at low temperature (40 K) to give aminomethanol (NH2CH2OH). We also show that in presence of HCOOH the warming of an ice mixture H2CO:NH3 gives at room temperature hexamethylenetetramine (HMT-C6H12N4). From an astrobiological point of view, HMT is of significant interest, since its hydrolysis leads to the formation of amino-acids. Furthermore, it is one of the main refractory products obtained after VUV photolysis at 10 K of ice mixtures containing CH3OH and NH3. It is also suspected to be a part of the organic matter present in comets and asteroids. In this contribution, we demonstrate that HMT can no longer be considered as a reliable indicator of VUV photolysis of ice, as we demonstrate that it can be formed from a purely thermal reaction

Formaldehyde and methylamine reactivity in interstellar ice analogues as a source of molecular complexity at low temperature

Context. Laboratory simulations on interstellar or cometary ice analogues are crucial to understand the formation of complex organic molecules that are detected in the interstellar medium (ISM). Results from this work give hints on physical and chemical processes occurring in space and can serve as a benchmark for dedicated space missions. Aims. The aim of this work is to consolidate the knowledge of ice evolution during the star formation process by investigating the influence of thermal reactions as a source of molecular complexity in the ISM. In this study, we are interested in the thermal reactivity between two interstellar molecules, formaldehyde (H2CO) and methylamine (CH3NH2) in water ice analogues. Methods. We used Fourier transform infrared spectroscopy, mass spectrometry, and B3LYP calculations to investigate the thermal reaction between formaldehyde and methylamine (14N and 15N) at low temperature in water ice analogues. Results. We demonstrate that methylamine and formaldehyde quickly react in water ice analogues for astronomically relevant temperatures and form N-methylaminomethanol CH3NHCH2OH. The measured activation energy of this reaction, 1.1 ± 0.05 kJ mol-1 (1.8 ± 0.08 kJ mol-1 with methylamine 15N), allows the reaction to proceed in interstellar ices, when the ices are gently warmed, as it occurs in young stellar objects, in photo-dissociation regions, or in comets. Therefore, CH3NHCH2OH is likely to be found in these objects. This hypothesis is confirmed by numerical simulations that clearly show that the formation of N-methylaminomethanol is likely at low temperature. Isotopic experiments as well as photochemical studies have also been performed to better characterise the ice evolution induced by heat and ultraviolet radiation during star formation

Influence of phyllosilicates on the hydrothermal alteration of organic matter in asteroids: Experimental perspectives

International audienceThe origin of the diverse organic compounds present in carbonaceous chondrites (CC) remains uncertain. We aim at investigating the role that hydrothermal alteration may have had on the molecular evolution of organic matter (OM). In particular, within CC matrices, OM is intimately embedded within phyllosilicates down to the nanometer scale, which raises the question of the influence of phyllosilicates on OM transformation during hydrothermal alteration on parent bodies. We conducted hydrothermal experiments at 150°C and alkaline pH, using a well-known molecule present in processed interstellar ice analogues, the hexamethylenetetramine (HMT), in the presence of Al- and Fe-rich smectites. Experimental products were characterized by gas chromatography mass spectrometry, infrared spectroscopy, X-ray diffraction and synchrotron-based X-ray absorption near edge structure spectroscopy. Within 31 days, the HMT+smectites+H2O system leads to (1) the formation of a diverse suite of soluble organic compounds, yet less abundant and less complex than in the absence of smectite, (2) carbon-rich smectite residues (3.8 wt.% and 2.6 wt.% of carbon for the Al- and Fe-rich smectite residues, respectively). In addition, the abundance and molecular composition of the final organic compounds depend on the nature of the phyllosilicate (Al vs. Fe-smectite). Various and complex interaction mechanisms could occur between OM and smectite. Physisorption, chemisorption and intercalation processes have likely entrapped a significant portion of the organic compounds, thereby altering their chemical evolution. The present work demonstrates that the presence and the nature of phyllosilicates influences the reaction pathways of organic compounds during hydrothermal alteration and that the presence of organic compounds may impact the mineral assemblage. This could have had significant importance for the co-evolution of OM and mineral phases in primitive bodies during hydrothermal alteration

Aminoacetonitrile characterization in astrophysical-like conditions

Context. Aminoacetonitrile (AAN) has been detected in 2008 in the hot core SgrB2. This molecule is of particular interest because it is a central molecule in the Strecker synthesis of amino acids. This molecule can be formed from methanimine (CH2NH), ammonia (NH3) and hydrogen cyanide (HCN) in astrophysical icy conditions. Nevertheless, few studies exist about its infrared (IR) identification or its astrophysical characterization. Aims. We present in this study a characterization of the pure solid AAN and when it is diluted in water to study the influence of H2O on the main IR features of AAN. The reactivity with CO2 and its photoreactivity are also studied and the main products were characterized. Methods. Fourier transformed infrared (FTIR) spectroscopy of AAN molecular ice was performed in the 10–300 K temperature range. We used temperature-programmed desorption coupled with mass spectrometry detection techniques to evaluate the desorption energy value. The influence of water was studied by quantitative FTIR spectroscopy and the main reaction and photochemical products were identified by FTIR spectroscopy. Results. We determined that in our experimental conditions, the IR limit of AAN detection in the water ice is about 1  ×  1016 molecule cm-2, which means that the AAN detection is almost impossible within the icy mantle of interstellar grains. The desorption energy of pure solid AAN is of 63.7 kJ mol-1 with ν0 to 1028 molecule cm-2 s-1, which implies that the presence of this molecule in the gas phase is only possible in hot cores. The glycine (Gly) formation from the AAN through the last step of the Strecker synthesis seems to be impossible in astrophysical-like conditions. Furthermore, AAN is photoresistant to vacuum ultra-violet radiation, which emphasizes the fact that AAN can be considered as a Gly reservoir molecule