Deuterated Ammonia in Galactic Protostellar Cores

We report on a survey of NH2D towards protostellar cores in low–mass star formation and quiescent regions in the Galaxy. Twenty–three out of thirty-two observed sources have significant (∼5σ) NH2D emission. Ion–molecule chemistry, which preferentially enhances deuterium in molecules above its cosmological value of 1.6× 10 sufficiently explains these abundances. NH2D/NH3 ratios towards Class 0 sources yields information about the “fossil remnants” from the era prior to the onset of core collapse and star formation. We compare our observations with predictions of gas–phase chemical networks. Subject headings: Molecular Processes; ISM: abundances; ISM: general; ISM: clouds; ISM: molecules; ISM:deuterium; radio lines: ISM