The Distribution of Deuterium in the ISM: One Nucleon is Never Enough

Abstract

The tendency for deuterium to be concentrated into the cold dense regions of the galaxy is due to the lower ground state energy of the heavier molecules. Such chemical fractionation leads to [D/H] values as high as 1! In turn this allows the detection of species such as ND_3, H_2D^+ and D_2H^+. The fraction of the interstellar medium (ISM) with such large deuteration is hard to estimate, but may be sufficient to cause both spatially variable and generally low [D/H] values in the diffuse ISM.

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