Mono- and di-deuterated ammonias: Far-infrared spectra and spectroscopic parameters in the ground state

•NH2D and ND2H transitions are identified in the high resolution far infrared spectra.•For NH2D, 2153 precise transitions in the ground state with J up to 24 are assigned.•For ND2H, 3214 precise transitions in the ground state with J up to 28 are assigned.•Watson-type S reduced Hamiltonian, representations IIIr and IIIl, was adopted.•The model successfully reproduces the transitions at experimental accuracy.