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Stability of CH3NCO in astronomical ices under energetic processing. A laboratory study

AutorMaté, Belén ; Molpeceres, Germán; Tanarro, Isabel ; Peláez, Ramón J. ; Guillemin, J. C.; Cernicharo, José ; Herrero, Víctor J.
Palabras claveAstrochemistry
Interstellar medium (ISM)
Kuiper Belt: general
Molecular data
Solid state: volatile
Fecha de publicación3-jul-2018
EditorAmerican Astronomical Society
CitaciónAstrophysical Journal 861(1): 61 (2018)
ResumenMethyl 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.
Versión del editorhttps://doi.org/10.3847/1538-4357/aac826
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