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Organic material found in meteorites and interplanetary dust particles isenriched in D and 15N. This is consistent with the idea that the functionalgroups carrying these isotopic anomalies, nitriles and amines, were formed byion-molecule chemistry in the protosolar nebula. Theoretical models ofinterstellar fractionation at low temperatures predict large enrichments inboth D and 15N and can account for the largest isotopic enrichments measured incarbonaceous meteorites. However, more recent measurements have shown that, insome primitive samples, a large 15N enrichment does not correlate with one inD, and that some D-enriched primitive material displays little, if any, 15Nenrichment. By considering the spin-state dependence in ion-molecule reactionsinvolving the ortho and para forms of H2, we show that ammonia and relatedmolecules can exhibit such a wide range of fractionation for both 15N and D indense cloud cores. We also show that while the nitriles, HCN and HNC, containthe greatest 15N enrichment, this is not expected to correlate with extreme Denrichment. These calculations therefore support the view that Solar System 15Nand D isotopic anomalies have an interstellar heritage. We also compare ourresults to existing astronomical observations and briefly discuss future testsof this model.

Isotopic Anomalies in Primitive Solar System Matter: Spin-state Dependent Fractionation of Nitrogen and Deuterium in Interstellar Clouds