October 2004


A number of interstellar features have been assigned to species trapped in ices that can form as mantles on dust grains. It was suggested than an IR feature at 2165 cm–1  (4.62 μm) observed initially in 1984 by Lacy et al. might be due to the cyanate ion (OCN ) as early as 1987 by Grim & Greenberg. However, a number of additional studies were needed to confirm this identification. Various experimental studies, including work by Demyk et al., Hudson et al., and Novozamsky et al., indicated that cyanate can be formed when isocyanic acid (HNCO) is trapped in an ice matrix, even at the very cold temperatures of dense interstellar clouds. If a strong base such as ammonia (NH3) is present in the proper proximity, a proton can transfer from HNCO to yield cyanate.

The figure to the right shows the asymmetric OCN stretching mode of cyanate as it appears within a cluster of 12 water molecules as computed quantum chemically. Note the ammonium ion that is coordinated to the N end of the anion. The calculations reproduced the stretching frequency as well as shifts observed in experiments where all H, N, C, or O was substituted with less common isotopes.

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