Combining the techniques of molecular beam and vacuum ultraviolet synchrotron radiation photoionization mass spectroscopy, we have measured the ionization energy of NH 3 (10.16±0.02 eV) and the appearance potentials of H + (18.57±0.05 eV) and NH 2 + (15.75±0.02 eV). From these data, we have obtained dissociation energy values for D 0(H 2NH) (4.97±0.05 eV), D 0(H 2N +H) (5.59±0.02 eV) and D 0(H 2NH +) (8.41±0.05 eV) and the ionization energy IE(NH 2) (10.78±0.05 eV). High-level ab initio calculations lead to results that are in good agreement with the experimental findings.