The microwave spectra of ( methylamino) thiophosphoryl difluoride, CH3NHP(=S)F-2, and two deuterated species, CH3NDP(=S)F-2 and CD3NHP(=S)F-2, have been investigated in the region from 26.5 to 39.0 GHz. The rotational constants of the ground vibrational state have been determined and have been shown to be only consistent with the trans conformer (CH3 group antiperiplanar to the P=S bond) with C-s symmetry. The a-type R branch transitions have been assigned for the trans conformer for the three isotopomers on the basis of the rigid rotor model. Near-trans and near-cis forms without molecular planes of symmetry are predicted by all ab initio calculations with the near-trans form being more stable. However, the double-well potentials governing the interchange between the two enantiomeric near-trans as well as the two near-cis forms are too shallow to accommodate the zero-point energies of the nu(24) asymmetric torsion. Thus, the trans conformation with C-s symmetry may be more accurate in explaining the microwave experimental data. The "adjusted" r(0) structural parameters have been obtained by systematically adjusting the ab initio MP2(full)/6-311+G(d,p) structure of the trans conformer with C-s symmetry to fit the microwave rotational constants. The determined heavy atom distances are r(C-N) = 1.459(5), r(P-N) = 1.621(5), r(P=S) = 1.879(5), and r(P-F) = 1.550(5) angstrom, and the heavy atom angles are angle CNP = 124.7(5)degrees, angle NPS = 118.3(5)degrees, angle NPF = 103.2(5)degrees, angle FPS = 117.0(5)degrees, and angle FPF = 94.6(5)degrees. The adjusted r(0) parameters have also been obtained for aminodifluoro-phosphine, H2NPF2, with a slightly pyramidal -PNH2 moiety. The results indicate that the previously reported short distance of 0.981(5) angstrom for the N-H-o(outer) bond from the microwave study is too short, and the adjusted r(0) value of 1.007(3) angstrom is obtained from the combined data. Adjusted r(0) parameters are also reported for (dimethylamino)difluorophosphine, (CH3)(2)NPF2, with C-s symmetry with the PNC2 portion of the molecule being planar. The previously reported C-H distances from the electron diffraction study are too long, and the angle PNCi and angle CoNCi angles are also found to be in error. These results provide a reasonable explanation why the microwave and electron diffraction results differ for the structures of these latter two molecules.