NITROGEN ISOTOPIC FRACTIONATION OF INTERSTELLAR NITRILES

In light of recent measurement of nitrogen isotope ratios in CN and HCN in several comets, and the correlation between (15)N excess and the presence of nitrile (-CN) functional groups in meteoritic samples, we have reassessed the potential of interstellar chemistry to directly fractionate nitriles. We focus in particular on the (15)N chemistry in selective depletion cores where O-bearing molecules are depleted yet N- and C-bearing species remain in the gas, as revealed by the recent detection of CN in dense CO-depleted cores. We show that large HC(15)N/HC(14)N ratios can be generated if the reaction of CN with N has a barrier, and suggest that cometary HCN and CN may trace material originally formed in dense interstellar clouds.