The observation of an abrupt predissociation threshold in an extremely congested electronic spectrum has been used to measure the bond dissociation energies of the mixed early-late transition metal molecules YCo, YNi, ZrCo, ZrNi, NbCo, and NbNi. In these systems it is argued that predissociation occurs as soon as the ground separated atom limit is exceeded, providing values of Di(YCo) = 2.591 f 0.001 eV, Di(YNi) = 2.904 f 0.001 eV, D:(ZrCo) = 3.137 f 0.001 eV, Di(ZrNi) = 2.861 f 0.001 eV, Di(NbCo) = 2.729 f 0.001 eV, and Di(NbNi) = 2.780 f 0.001 eV. In addition, the bond strength of diatomic zirconium has been measured as Di(Zr,) = 3.052 f 0.001 eV. A discussion of the chemical bonding in the mixed early-late transition metal dimers and Zr1 is presented, based on the measured bond energies of these species. I. Introduction The chemical bonding between transition metal atoms is an area of interest to many different branches of chemistry, including metallurgy, surface science, and metal cluster chemistry. Unraveling the details of the complicated electronic structure in these metallic species is an ongoing process pursued through both experimental1.2 and theoreticaP4 avenues. From this research it is already clear that several distinct factors combine to determine thestrength and character of the chemical bond between transition metal atoms. One such factor is the loss of exchange energy which occurs upon formation of d-electron bonds, thereby reducing the strength of the chemical bonding. This is illustrated in the example of Ti2,5 where exchange effects favor the 4sui3d~:3du:3d6:, 3As,, state as a candidate for the ground state, while bonding considerations favor the 4sui3d?r~3du~, IZ; state. In Ti2 the balance between exchange effects and chemical bonding is so delicate that ab initio theory is incapable of determining which possibility is the ground state.5 Experimentally it is found that exchange effects dominate in Tiz, leading to an X 3$,, ground state.6 In the isovalent Zr2 molecule, however, the larger d-orbitals favor bond formation, leading to a strong theoretical prediction of a '2: ground Thus, to understand the bonding in the diatomic transition metals the competing effects of exchange and chemical bonding must be carefully considered.