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Etude par spectrométrie IRTF de la réactivité de l'acide isocyanique (HNCO) avec des glaces composées d'eau et d'ammoniac: Production spontanée de l'ion OCN- dans le milieu interstellaire

Abstract : The interstellar ices are mainly composed of CO, H2O, NH3, .... Under a luminous flow coming from stars (λ > 120 nm) these ices are subjected to photochemical processing and can evolve to the formation of new and more complex products. Among them, the isocyanic acid (HNCO) is found which we have studied the reactivity with H2O, NH3 and NH3/H2O ices. We have shown that it was been at the origin of the OCN- formation. This ion can be characterised by ISO spectra of protostellar sources, from its band at 4,62 μm (2167 cm-1). A spontaneous production of OCN-, in agreement with the temperature range (10 - 100 K) which ices evolve, is produced when HNCO and NH3 in excess are codeposed at 10 K. A salt analogous at NH4+OCN- is formed at above 160 K. Quantum calculations have shown that solvation of NH3 molecule in direct interaction with HNCO by three other NH3 molecules, plays an important role into the NH4+ and OCN- formation process and confirm the spontaneous character of this reaction. The UV irradiation (λ > 120 nm) of solid HNCO leads to the OCN- formation but also carbonyl compounds as formaldehyde, formamide, and urea. The comparison of the primary photoproducts spectrum with ISO spectrum of NGC7538 IRS9 or W33A ices, could give a tentative attribution for the bands located at 1700 cm-1 and 1470 cm-1.
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Submitted on : Friday, July 1, 2005 - 2:59:44 PM
Last modification on : Thursday, January 18, 2018 - 2:26:39 AM
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Sébastien Raunier. Etude par spectrométrie IRTF de la réactivité de l'acide isocyanique (HNCO) avec des glaces composées d'eau et d'ammoniac: Production spontanée de l'ion OCN- dans le milieu interstellaire. Autre. Université de Provence - Aix-Marseille I, 2003. Français. ⟨tel-00009640⟩

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