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Stability of CH3NCO in Astronomical Ices under Energetic Processing: A Laboratory Study

Abstract : Methyl isocyanate (CHNCO) was recently found in hot cores and suggested 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 CHNCO and of CHNCO(4-5%)/HO mixtures deposited at 20 K were irradiated with a UV D lamp (120-400 nm) and bombarded by 5 keV electrons to mimic the secondary electrons produced by cosmic rays (CRs). The destruction of CHNCO was studied using IR spectroscopy. After processing, the ν-NCO band of CHNCO disappeared and IR bands corresponding to CO, CO, 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 for CHNCO in water-ice), but not so good against high-energy electrons (half-life dose ~ 18 eV molecule). It was also found that CHNCO does not react with HO over the 20-200 K temperature range. These results indicate that hypothetical CHNCO in the ices of dense clouds should be stable against UV photons and relatively stable against CRs over the lifetime of a cloud (~ 10 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, both by photons and CRs, but embedded below just 10 μm of water-ice, the molecule could survive for ~ 10 yr.
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https://hal-univ-rennes1.archives-ouvertes.fr/hal-01861425
Contributor : Laurent Jonchère <>
Submitted on : Friday, August 24, 2018 - 2:30:24 PM
Last modification on : Friday, July 10, 2020 - 4:05:44 PM

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B. Mate, G. Molpeceres, I. Tanarro, R. J. Pelaez, J. C. Guillemin, et al.. Stability of CH3NCO in Astronomical Ices under Energetic Processing: A Laboratory Study. The Astrophysical Journal, American Astronomical Society, 2018, 861 (1), ⟨10.3847/1538-4357/aac826⟩. ⟨hal-01861425⟩

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