Doubly Deuterated Molecular Species in Protostellar Environments

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Abstract
We report the detection of the doubly deuterated forms of ammonia (ND2H) and formaldehyde (D2CO) toward 16293E, a newly identified low-luminosity protostar in the ρ Ophiucus molecular complex. The abundances of ND2H and D2CO compared with their hydrogenated counterparts NH3 and H2CO are ~3% and 40% ± 20%, respectively. To date, 16293E is thus the source with the highest levels of multiple deuteration: [ND2H]/[NH3] is 5-6 times larger there than in the only other astronomical source where ND2H has ever been found, the dense ammonia core of L134N; and [D2CO]/[H2CO] is more than 5 times higher than in the proto-binary system IRAS 16293-2422. The relative abundances of doubly deuterated molecules in low-luminosity protostars are much higher than their current gas-phase [D]/[H] ratios would suggest and, therefore, likely reflect active grain surface chemistry followed by some desorption process.