The single-photon zero kinetic energy (ZEKE) photoelectron spectra of the silver- and copper-ammonia 1:1 complexes have been observed in order to investigate the vibrational structures of their corresponding ions. The adiabatic ionization potentials (I.P.) of AgNH3 (47 580 cm(-1)) and CuNH3 (46 468 cm(-1)) decrease from those of the free metal atoms by 1.68 and 1.97 eV, respectively. The intermolecular stretching frequencies of the ionized complexes were determined to be 375 cm-1 for Ag+NH3 and 470 cm-1 for Cu+NH3. These observations indicate that the Cu+-NH3 binding is stronger than the Ag+-NH3 binding, consistent with the previous collision induced dissociation experiments. The binding energy of CuNH3 is found to be larger than that of AgNH3 in the neutral state as well from the observed I.P. shifts and the binding energies of the ionized complexes. This is also consistent with the smaller redshift of the origin band of CuNH3 on deuteration and the Franck-Condon intensity patterns observed in the ZEKE spectra. The stronger Cu-NH3 bonding in the neutral complex is attributed to the more efficient sd hybridization in the Cu atom. (C) 2003 American Institute of Physics.