Astrophys. J., 861, 61-61 (2018/July-1)
Stability of CH3NCO in astronomical ices under energetic processing: a laboratory study.
MATE B., MOLPECERES G., TANARRO I., PELAEZ R.J., GUILLEMIN J.C., CERNICHARO J. and HERRERO V.J.
Abstract (from CDS):
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.
© 2018. The American Astronomical Society. All rights reserved.
astrochemistry - interstellar medium ISM - Kuiper Belt: general - molecular data - solid state: volatile
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