Removal of neutral O-atoms from a transition metal (TM) oxide results in two electrons residing within the vacated site. Two-electron multiplet theory has been used to develop a d 2 equivalent model. When applied to tetragonal HfO 2 , the two electrons of neutral vacancy in the d 2 equivalent limit reside on two Hf d-state orbitals in a high-spin configuration. Transition energies and negative ion state features are detected in transition metal (TM) oxides by X-ray absorption spectroscopy (XAS) in the O K preedge/sub-band gap energy regime, and are compared with the model. These transitions are from the O 1s 2 doubly occupied core level approximately 543 eV below vacuum, and terminate in empty virtual bound states. In addition these strong spin-allowed transitions, spectra include weaker features corresponding to either spin-forbidden transitions in the d 2 model, or alternatively to a near-degeneracy with a singlet ground state with weak Hf-atom pair bonds. The analysis of O K edge XAS spectra identify a significant distinction between multiplet (i) triplet transition energies for neutral O-vacancies that are not active as electron or hole traps, (ii) O-vacancy negative ion states that are active as electron traps in Poole-Frenkel conduction or trap-assisted tunneling (TAT), and (iii) O-vacancy occupied ground states that can trap holes.