Interstellar processes leading to molecular deuterium enrichment and their detection

Large deuterium (D) enrichments in meteoritic materials indicate that interstellar organic materials survived incorporation into parent bodies within the forming Solar System. These enrichments are likely due to one or more of four distinct astrochemical processes. These are (i) low-temperature gas phase ion–molecule reactions, (ii) low-temperature gas–grain reactions, (iii) gas phase photodissociation, and (iv) ultraviolet photolysis in D-enriched ice mantles. Each of these processes should be associated with molecular carriers having distinct structural signatures (D placement on the product molecules, correlation with specific chemical functionalities, etc.). These processes are reviewed and specific spectroscopic signatures for the detection of these processes in space are identified and described.