Extensive DFT calculations are performed to optimize the geometric structures of O-rich tungsten oxide clusters, to simulate the PES spectra, and to analyze the chemical bonding. The ground-state structure of W4O14^- is best considered as W4O12（O2^-）, containing a side-on bound superoxide ligand. The current study indicates that the extra electron in W4O12^- is capable of activating dioxygen by non-dissociative electron transfer （W 5d → O2 π^＊）, and the anionic clusters can be viewed as models for reduced defect sites on tungsten oxide surfaces for the chemisorption of O2.
