Deuterated ammonia in Galactic massive star-forming regions
  We present sensitive observations of NH2D at 110.153599 GHz toward 50
Galactic massive star-forming regions with IRAM 30-m telescope. The NH2D
transition is detected toward 36 objects, yielding a detection rate of 72%.
Column densities of NH2D, HC3N and C18O for each source are derived by assuming
local thermal equilibrium conditions with a fixed excitation temperature. The
deuterium ratio of NH$_3$, defined as the abundance ratio of NH2D to NH3, for
19 sources is also obtained with the information of NH3 from the literature.
The range of deuterium fractionation bends to be large in the late-stage
star-forming regions in this work, with the value from 0.043 to 0.0006. The
highest deuterium ratio of NH3 is 0.043 in G081.75+00.78 (DR21). We also find
that the deuterium ratio of NH3 increases with the Galactocentric distances and
decreases with the line width.
