Ground and low-lying excited state properties of the first-row transition-metal oxide diatomics calculated by an improved ASED-MO model

The ground and selected low-lying electronic states of the entire series of the first-row transition-metal neutral oxides are investigated by the use of an improved atom superposition and electron delocalization molecular orbital (ASED-MO) approach. Two quantities are found to be very important in achieving agreement with experiment: these are the (kappa,delta) parameter set - involved in the Wolfsberg-Helmholz constant, K - and the charge dependent Slater-type orbital exponents. For SeO through CrO the optimum (kappa,delta) set of (0.87, 0.24 Angstrom(-1)) yields ground states and spectroscopic constants (R(e), D-0, omega(e) and mu) in good agreement with experiment. The set (1.00, 0.35 Angstrom(-1)) works well for MnO to CuO and (0.75, 0.13 Angstrom(-1)) for ZnO. Calculations are consistent with both ionic and covalent bonding contributions in the monoxides. The M-O bond strengths exhibit the ''double humped'' shape, characteristic of many periodic properties of the transition metals. Moreover, the sharp contrast in the calculated bond energies between the early and late transition-metal oxides accounts well for the pronounced differences in their reactivities.