The 15N-enrichment in dark clouds and Solar System objects
  The line intensities of the fundamental rotational transitions of H13CN and
HC15N were observed towards two prestellar cores, L183 and L1544, and lead to
molecular isotopic ratios 140 6 14N/15N 6 250 and 140 6 14N/15N 6 360,
respectively. The range of values reflect genuine spatial variations within the
cores. A comprehensive analysis of the available measurements of the nitrogen
isotopic ratio in prestellar cores show that molecules carrying the nitrile
functional group appear to be systematically 15N-enriched com- pared to those
carrying the amine functional group. A chemical origin for the differential
15N-enhance- ment between nitrile- and amine-bearing interstellar molecules is
proposed. This sheds new light on several observations of Solar System objects:
(i) the similar N isotopic fractionation in Jupiter's NH3 and solar wind N+;
(ii) the 15N-enrichments in cometary HCN and CN (that might represent a direct
inter- stellar inheritance); and (iii) 15N-enrichments observed in organics in
primitive cosmomaterials. The large variations in the isotopic composition of
N-bearing molecules in Solar System objects might then simply reflect the
different interstellar N reservoirs from which they are originating.
