Analyses of the ScO- and ScO2- photoelectron spectra

We have optimized geometries for various electronic states of both neutral and anionic ScO and ScO2 using density functional theory (DFT) and coupled cluster theory. Adiabatic and vertical separation energies have been computed using both DFT and coupled cluster theory. For the ScO- anion the (1)Sigma(+) state is predicted to lie lower than the (3)Delta state by 1.48 eV. In fact, the anion (3)Delta state is higher in energy than the (2)Sigma(+) neutral ground state. This contradicts the assignment of the ScO- ground state made by Wu and Wang, in their recent report of photoelectron spectroscopy experiments. The CCSD(T) adiabatic electron affinity for the ground state of ScO is 1.30 eV, while the vertical detachment energy is 1.33 eV. This compares favorably with the experimental value of 1.35 eV. For ScO2 the B-2(2) ground state with a CCSD(T) bond angle of 140.5 degrees is lower in energy than the (2)A(1) state with a bond angle of 48.4 degrees by 1.13 eV. The anion minima include two (1)A(1) states, with the CCSD(T) global minimum corresponding to 140.9 degrees and the 2.00 eV higher energy state having a bond angle of 47.4 degrees. For ScO2 the adiabatic electron affinity was computed with CCSD(T) to be 2.22 eV with a corresponding vertical detachment energy of 2.30 eV. This compares with an experimental vertical detachment of 2.32 eV. (C) 2000 American Institute of Physics. [S0021-9606(00)30526-8].