An Interstellar Trifecta

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Science  14 Jun 2002:
Vol. 296, Issue 5575, pp. 1931-1933
DOI: 10.1126/science.296.5575.1931e

In the emptiness of interstellar space, very cold, very dense, and very dark molecular clouds hide important and unusual molecular species that condense onto icy dust grains; these mysterious clouds may also harbor the beginnings of star formation. Identifying the condensed species and the chemical processes (many of which do not occur in the terrestrial environment) that produce them is critical for assessing the elemental abundances in the interstellar medium, but Earth-based observations favor detection of energetic molecules in the gaseous phase.

It comes as a surprise, therefore, that Lis et al. and van der Tak et al. have found triply deuterated ammonia, ND3, in the Barnard 1 and NGC 1333 clouds by using high-resolution spectroscopy at the Caltech Submillimeter Observatory. Modeling suggests that ND3 may be formed from a series of ion-molecule reactions in the gas phase because hydrogen has a higher probability than deuterium of being ejected after partially deuterated ions collide. ND3 may also arise from grain surface chemistry and be converted to a gaseous phase by youthful radiation from a protostellar wind. The gas phase D/H for this pathway would be much higher than expected, requiring new models of the chemistry of star formation. — LR

Astrophys. J.571, L55 (2002); Astron. Astrophys., in press (astro-ph/0204448)

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