Gas-phase production of NHD2 in L134N

We show analytically that large abundances of NH2D and NHD2 can be produced by gas-phase chemistry in the interiors of cold dense clouds. The calculat ed fractionation ratios are in good agreement with the values that have bee n previously determined in L134N and suggest that triply deuterated ammonia could be detectable in dark clouds. Grain-surface reactions may lead to si milar NH2D and NHD2 enhancements but, we argue, are unlikely to contribute to the deuteration observed in L134N.