SIMBAD references

We present sensitive observations of NH₂D 1₁₁^a-1₀₁^s at 110.153 599 GHz toward 50 Galactic massive star-forming regions with the Institut de Radioastronomie Millimetrique (IRAM) 30-m telescope. The NH₂D 1₁₁^a-1₀₁^s transition is detected toward 36 objects, yielding a detection rate of 72 per cent. 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 NH₃, defined as the abundance ratio of NH₂D to NH₃, for 19 sources is also obtained with the NH₃ information 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 Galactocentric distance and decreases with line width.