The HNC/HCN ratio in comets: Observations of C/2002 C1 (Ikeya-Zhang) Original Research Article

We have observed HNC and HCN in the coma of comet C/2002 C1 (Ikeya-Zhang). We derive HNC/HCN ratios of 23 per cent and 3 percent at heliocentric distances of 0.73 and 0.96 AU respectively. These amounts of HNC cannot be synthesised in the coma via bimolecular chemical reactions, and so these observations appear to confirm that the dominant source of HNC in cometary comae is the degradation of complex organic material.