Suchergebnisse

Methyl isocyanate (CH3NCO) was recently found in hot cores and suggested to exist on comet 67P/CG. The incorporation of this molecule into astrochemical networks requires data on its formation and destruction. In this work, ices of pure CH3NCO and of CH3NCO(4%–5%)/H2O mixtures deposited at 20 K were irradiated with a UV D2 lamp (120–400 nm) and bombarded by 5 keV electrons to mimic the secondary electrons produced by cosmic rays (CRs). The destruction of CH3NCO was studied using IR spectroscopy. After processing, the νa–NCO band of CH3NCO disappeared and IR bands corresponding to CO, CO2, OCN−, and HCN/CN− appeared instead. The products of photon and electron processing were very similar. Destruction cross sections and half-life doses were derived from the measurements. Water ice provides a good shield against UV irradiation (half-life dose of ∼64 eV molecule−1 for CH3NCO in water ice), but is not so good against high-energy electrons (half-life dose ∼18 eV molecule−1). It was also found that CH3NCO does not react with H2O over the temperature range 20–200 K. These results indicate that hypothetical CH3NCO in the ices of dense clouds should be stable against UV photons and relatively stable against CRs over the lifetime of a cloud (∼107 yr), and could sublime in the hot core phase. On the surface of a Kuiper Belt object (the original location of comet 67P/CG) the molecule would be swiftly destroyed, by both photons and CRs, but embedded below just 10 μm of water ice, the molecule could survive for ∼109 yr. ; This work has been funded by the Spanish MINECO under grants FIS2013-48087-C2-1P, FIS2016-C3-1P, and AYA2016- 75066-C2-1-P. J.-C.G. and J.C. also thank the ANR-13-BS05- 0008 IMOLABS and J.-C.G. thanks the Program PCMI (INSU-CNRS) and the Centre National d'Etudes Spatiales (CNES) for funding support. European Union funding under grant ERC-2013-Syg 610256 (NANOCOSMOS) is also acknowledged. ; Peer reviewed

10 pags., 9 figs., 2 tabs. ; Interstellar (IS) dust analogs, based on amorphous hydrogenated carbon (a-C:H) were generated by plasma deposition in radio frequency discharges of CH4 + He mixtures. The a-C:H samples were characterized by means of secondary electron microscopy, infrared (IR) spectroscopy and UV-visible reflectivity. DFT calculations of structure and IR spectra were also carried out. From the experimental data, atomic compositions were estimated. Both IR and reflectivity measurements led to similar high proportions (≈50%) of H atoms, but there was a significant discrepancy in the sp2/sp3 hybridization ratios of C atoms (sp2/sp3 = 1.5 from IR and 0.25 from reflectivity). Energetic processing of the samples with 5 keV electrons led to a decay of IR aliphatic bands and to a growth of aromatic bands, which is consistent with a dehydrogenation and graphitization of the samples. The decay of the CH aliphatic stretching band at 3.4 μm upon electron irradiation is relatively slow. Estimates based on the absorbed energy and on models of cosmic ray (CR) flux indicate that CR bombardment is not enough to justify the observed disappearance of this band in dense IS clouds. ; This work was funded by the Spanish MINECO under grants FIS2013-48087-C2-1P and FIS2016-77726-C3-1P. European Union funding under the project ERC-2013-Syg 610256 (NANOCOSMOS) is also acknowledged. ; Peer reviewed

13 pags., 8 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0 ; The increasing demand for nanostructured materials is mainly motivated by their key role in a wide variety of technologically relevant fields such as biomedicine, green sustainable energy or catalysis. We have succeeded to scale-up a type of gas aggregation source, called a multiple ion cluster source, for the generation of complex, ultra-pure nanoparticles made of different materials. The high production rates achieved (tens of g/day) for this kind of gas aggregation sources, and the inherent ability to control the structure of the nanoparticles in a controlled environment, make this equipment appealing for industrial purposes, a highly coveted aspect since the introduction of this type of sources. Furthermore, our innovative UHV experimental station also includes in-flight manipulation and processing capabilities by annealing, acceleration, or interaction with background gases along with in-situ characterization of the clusters and nanoparticles fabricated. As an example to demonstrate some of the capabilities of this new equipment, herein we present the fabrication of copper nanoparticles and their processing, including the controlled oxidation (from Cu to CuO through CuO, and their mixtures) at different stages in the machine. ; This work was supported by the European Union [grant number ERC-2013-SyG 610256 NANOCOSMOS]; the Spanish MINECO [grant numbers MAT2017-85089-C2-1-R, MAT2014-54231-C4-1-P, MAT2014-54231- C4-4-P, MAT2014-59772-C2-2-P, FIS2016-77578-R, FIS2013-48087-C2-1P, FIS2016-77726-C3-1P and CSIC13-4E-1775]. ; Peer Reviewed

I. Tanarro et al. -- 16 pags., 18 figs., app. ; We present a proof of concept on the coupling of radio astronomical receivers and spectrometers with chemical reactors and the performances of the resulting setup for spectroscopy and chemical simulations in laboratory astrophysics. Several experiments including cold plasma generation and UV photochemistry were performed in a 40 cm long gas cell placed in the beam path of the Aries 40 m radio telescope receivers operating in the 41–49 GHz frequency range interfaced with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz resolution. The impedance matching of the cell windows has been studied using di erent materials. The choice of the material and its thickness was critical to obtain a sensitivity identical to that of standard radio astronomical observations. Spectroscopic signals arising from very low partial pressures of CH3OH, CH3CH2OH, HCOOH, OCS, CS, SO2 (<103 mbar) were detected in a few seconds. Fast data acquisition was achieved allowing for kinetic measurements in fragmentation experiments using electron impact or UV irradiation. Time evolution of chemical reactions involving OCS, O2 and CS2 was also observed demonstrating that reactive species, such as CS, can be maintained with high abundance in the gas phase during these experiments ; The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC-SyG-2013 Grant Agreement No. 610256 NANOCOSMOS and from spanish MINECO CSD2009-00038 (ASTROMOL) under the Consolider-Ingenio Program. We also thank spanish MINECO for funding under grants AYA2012-32032, AYA2016-75066-C2-1-P, FIS2013-48087-C2-1-P, FIS2016-77726-C3-1-P, FIS2016-77578-R, MAT2014- 54231-C4-1-P. ; Peer reviewed