Investigation of HNCO isomers formation in ice mantles by UV and thermal processing: an experimental approach

Abstract

Current gas phase models do not account for the abundances of HNCO isomers detected in various environments, suggesting a formation in icy grain mantles. We attempted to study a formation channel of HNCO and its possible isomers by vacuum-UV photoprocessing of interstellar ice analogues containing H${}_2$O, NH${}_3$, CO, HCN, CH${}_3$OH, CH${}_4$, and N${}_2$ followed by warm-up, under astrophysically relevant conditions. Only the H${}_2$O:NH${}_3$:CO and H${}_2$O:HCN ice mixtures led to the production of HNCO species. The possible isomerization of HNCO to its higher energy tautomers following irradiation or due to ice warm-up has been scrutinized. The photochemistry and thermal chemistry of H${}_2$O:NH${}_3$:CO and H${}_2$O:HCN ices was simulated using the Interstellar Astrochemistry Chamber (ISAC), a state-of-the-art ultra-high-vacuum setup. The ice was monitored in situ by Fourier transform mid-infrared spectroscopy in transmittance. A quadrupole mass spectrometer (QMS) detected the desorption of the molecules in the gas phase. UV-photoprocessing of H${}_2$O:NH${}_3$:CO/H${}_2$O:HCN ices lead to the formation of OCN${}^{-}$ as main product in the solid state and a minor amount of HNCO. The second isomer HOCN has been tentatively identified. Despite its low efficiency, the formation of HNCO and the HOCN isomers by UV-photoprocessing of realistic simulated ice mantles, might explain the observed abundances of these species in PDRs, hot cores, and dark clouds.

References in corpus (2)

• Discovery of Fulminic Acid, HCNO, in Dark Clouds
• Vacuum-UV spectroscopy of interstellar ice analogs. I. Absorption cross-sections of polar-ice molecules

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