PNNL

Abstract

We report a comparative study of reduced transition metal oxide clusters, M3O8- (M = Cr, W) anions and their neutrals, via anion photoelectron spectroscopy (PES) and density functional theory (DFT) and molecular orbital theory (CCSD(T)) calculations. Well-resolved PES spectra are obtained for M3O8- (M = Cr, W) at 193 and 157 nm photon energies. Different PES spectra are observed for M = Cr versus M = W. Extensive DFT and CCSD(T) calculations are performed to locate the ground and low-lying excited states for the neutrals and anions. The ground states of Cr3O8 and Cr3O8- are predicted to be the 3B2 and 4B2 states of a C2v structure, respectively, revealing ferromagnetic spin coupling for Cr 3d electrons. In contrast, the ground states of W3O8 and W3O8- are predicted to be the 1A- state (Cs symmetry) and the 2A1 state (C2v symmetry), respectively, showing strong metal-metal d-d bonding in the anion. The current cluster geometries are in qualitative agreement with prior DFT studies at the PBE level for M = Cr and the B3LYP level for M = W. The BP86 and PW91 functionals significantly outperform the B3LYP functional for the Cr species, in terms of relative energies, electron detachment energies, and electronic excitation energies; whereas the B3LYP functional is better for the W species. In addition, accurate heats of formation for the ground states of M3O8 are calculated from the clustering energies and the heats of formation of MO2 and MO3.