Rotational spectra of the Ar-ND3 van der Waals complex were measured in the frequency range between 4 and 19 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. The isotopomers studied include those with ND3, NHD2, and NH2D. A tunneling splitting due to the inversion of the ammonia subunit within the ground state of the complex was observed for all three isotopomers. This splitting cannot be measured in Ar-NH3 for spin statistical reasons. Nuclear quadrupole hyperfine structure of rotational transitions arising from the N-14 nucleus was resolved and the corresponding nuclear quadrupole coupling constants were determined. A smaller nuclear quadrupole splitting arising from the deuterium nuclei was observed but not resolved. The ground state spectroscopic constants are compared with experimental and theoretical data previously reported for Ar-NH3. Additional transitions were observed for Ar-ND3 and assigned to the two inversion tunnelling states of an excited internal rotor state. A fit of the spectroscopic constants for these two states suggests the presence of a Coriolis perturbation along the lines of that observed in the microwave spectrum of Ar-NH3. (C) 2001 American Institute of Physics.