Detection of interstellar DNC: difficulties of chemical equilibrium hypothesis for enrichment

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Abstract
The J = 1 → 0 transition of DNC at 76.3058 GHz has been observed in emission in NGC 2264. Comparison with previous observations of HN13C indicates that deuterium is enriched in DNC similarly to the enrichment reported for DCO+ in this source. The DNC/HNC ratio is estimated to be about 1/24. The results cannot readily be interpreted in terms of chemical equilibria relating to the formation of DNC. It is suggested that the explanation must be sought in isotope effects on rates of formation of interstellar molecules.