Theoretical Study of Transition - Metal Hydrides . 5 . HfH + through HgH + , BaH ' , and LaH +

We present ab initio calculations (generalized valence bond plus configuration interaction, using relativistic effective core potentials) on the monopositive diatomic metal hydride ions of the third transition-metal series ( H M + through HgH+ plus BaH+ and LaH+). We analyze the trends in bond energies, equilibrium geometries, bond character, and excitation energies in terms of ( 1 ) the atomic configuration of the metal, (2) the orbital sizes of the metal, and (3) the exchange and promotion energies on bonding hydrogen to the high-spin metal. The bond dissociation energies are found to be significantly larger than in either firstor second-row transition-metal hydride cations.