Kinetics of the OCN− and HOCN formation from the HNCO + H2O thermal reaction in interstellar ice analogs
Résumé
Aims. We study in the laboratory the kinetics of the low-temperature OCN − and HOCN formation from the purely thermal reaction of solid HNCO and H 2 O. The cyanate ion OCN − is an intermediate in the isomerization process of isocyanic acid HNCO into cyanic acid HOCN in water ice. Methods. We study the reaction, isomerization and desorption kinetics of the HNCO/OCN − /HOCN system using Fourier transform infrared spectroscopy. Results. Activation energies of 26 ± 2 kJ mol −1 (3127 K) and 36 ± 1 kJ mol −1 (4330 K) are found for the HNCO + H 2 O → OCN − + H 3 O + and OCN − + H 3 O + → HOCN + H 2 O reactions respectively. Desorption energies of 37 ± 3 kJ mol −1 (4450 K) and 40 ± 3 kJ mol −1 (4811 K) are measured for HNCO and OCN − , respectively. Conclusions. The present experiment has the important implication that the H 2 O + HNCO reaction alone cannot account for the observed abundances of solid OCN − in astronomical IR sources.
Domaines
Chimie analytique
Origine : Fichiers produits par l'(les) auteur(s)
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