Atomic and Molecular Chemisorption of Oxygen in WO4- Clusters

Density functional theory (DFT) calculations were performed to study the monotungsten-oxide WO4 cluster in the anionic and neutral charge states. The results show the two most stable WO4- isomers have C2v and D2d symmetries and both have the four oxygen atoms attached to the tungsten W monomer atomically. The WO4- species previously suggested with a molecular adsorption of di-oxygen is found to be a metastable isomer of WO4-, whose geometric, vibrational properties and electron affinities are in good agreement with the ultraviolet photoelectron spectroscopy (UPS) experimental results. The reason why this metastable isomer could be observed in the experiment is given by a molecule formation mechanism. The UPS spectrums compare well with the excitation spectrum computed by time-dependent DFT method.