InNH3 has been studied with single-photon zero electron kinetic energy (ZEKE) spectroscopy and density functional theory and ab initio calculations. The ZEKE spectrum reveals vibrational structures of the cation and neutral complexes. The comparison of the experiment and theory establishes that the indium-ammonia complex is a simple adduct. The adduct has a C-3 nu (1)A(1) ground state in the ion and a C(s)(2)A' ground state in the neutral. The lower symmetry of the neutral molecule arises from a Jahn-Teller distortion. The ionization energy of the (2)A' state is 39 689(3) cm(-1). The indium-ammonia stretch frequency is 234 cm(-1) in the (1)A(1) state and 141 cm(-1) in the (2)A' state. The stronger metal-ligand bonding in the ion state is attributed to the additional charge-dipole and covalent interactions.