The ammonia-hydrogen bromide and ammonia-hydrogen iodide, anionic heterodimers were studied by anion photoelectron spectroscopy. In complementary studies, these anions and their neutral counterparts were also investigated via ab initio theory at the coupled cluster level. In both systems, neutral NH 3?HX dimers were predicted to be linear, hydrogen-bonded complexes, whereas their anionic dimers were found to be protontransferred species of the form, (NH4+X-)-. Both experimentally measured and theoretically predicted vertical detachment energies (VDE) are in excellent agreement for both systems, with values for (NH4+Br-)- being 0.65 and 0.67 eV, respectively, and values for (NH4-I-)- being 0.77 and 0.81 eV, respectively. These systems are discussed in terms of our previous study of (NH4-Cl-)-. © 2010 American Chemical Society.