HNCO Isomers Formation in Ice Mantles by UV and Thermal Processing

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 H2 O, NH3 , CO, HCN, CH3 OH, CH4 , and N2 followed by warm-up, under astrophysically relevant conditions. Only the H2 O:NH3 :CO and H2 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 H2 O:NH3 :CO and H2 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 H2 O:NH3 :CO/H2 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.

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

A. Jiménez-Escobar, B. M. Giuliano, G. M. Muñoz Caro, J. Cernicharo, N. Marcelino (Submitted on 4 Jul 2014)

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Astrophysics of Galaxies (astro-ph.GA); Chemical Physics (physics.chem-ph)

Journal reference: 2014 ApJ 788 19

DOI: 10.1088/0004-637X/788/1/19

Cite as: arXiv:1407.1242 [astro-ph.IM]  (or arXiv:1407.1242v1 [astro-ph.IM] for this version)

Submission history From: Barbara Michela Giuliano Dr. [v1] Fri, 4 Jul 2014 14:25:42 GMT (1178kb,D)

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