2011A&A...530A..96T

We study in the laboratory the kinetics of the low-temperature OCN^– and HOCN formation from the purely thermal reaction of solid HNCO and H₂O. The cyanate ion OCN^– is an intermediate in the isomerization process of isocyanic acid HNCO into cyanic acid HOCN in water ice. We study the reaction, isomerization and desorption kinetics of the HNCO/OCN^–/HOCN system using Fourier transform infrared spectroscopy. Activation energies of 26±2kJ/mol (3127K) and 36±1kJ/mol (4330K) are found for the HNCO+H₂O->OCN^–+H₃O⁺ and OCN^–+H₃O⁺->HOCN+H₂O reactions respectively. Desorption energies of 37±3kJ/mol (4450K) and 40±3kJ/mol (4811K) are measured for HNCO and OCN^–, respectively. The present experiment has the important implication that the H₂O + HNCO reaction alone cannot account for the observed abundances of solid OCN^– in astronomical IR sources.