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The D/H Ratio in Molecular Clouds

Published online by Cambridge University Press:  07 August 2017

A.G.G.M. Tielens
A.G.G.M. Tielens*
Affiliation:
MS 245-3, NASA Ames Research Center, Moffett Field, CA 94035, USA.

Abstract

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This paper summarizes our understanding of the dominant D-reservoirs in molecular clouds and suggests possible direct determinations of the D-abundance. It is concluded that rotational HD lines from shock regions provide the best way to determine the gas phase D-abundance. In cold dense cores, the dominant gas phase D-reservoir is likely to be atomic D, because of expected inefficient HD formation on grain surfaces. The gas phase D-abundance derived from observations of dense cores is ≍5 × 10-6/n4 (with n4 the total density in units of 104 cm−3). A large fraction of the D (≍50%) may be locked up in deuterated molecules in grain mantles. A small fraction (≍2%) may be locked up in the photolyzed residues of such grain mantles. PAHs will also be deuterated (PADs), containing ≍1% of the D. Finally, it is likely that all of these processes have contributed to the D-enrichment observed in solar system materials.

Type
Early Universe
Information
Symposium - International Astronomical Union , Volume 150: Astrochemistry of Cosmic Phenomena , 1992 , pp. 91 - 95
Copyright
Copyright © Kluwer 1992 

References

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