Electronic structure of dichalcogenide and dipnictide anions

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The Self-Consistent-Field Xα Scattered Wave Cluster MO method is used to calculate molecular orbital energy level diagrams for O 2, O 2 −, O 2 2−, S 2, S 2 2−, Se 2 2−, P 2 4−, As 2 4− and AsS 3−. Calculated energies are in good agreement with those measured by photoemission spectroscopy for O 2, S 2, S 2 2− in ZrS 3, Se 2 2− in ZrSe 3 and P 2 4− in TiP 2. For O 2 − the calculated energy of the π u → π g transition agrees fairly well with that of the UV absorption observed in LiO 2. The predicted photoemission spectrum of O 2 2− is consistent with a preliminary study on BaO 2. Calculated valence region widths in peroxides are found to be significantly greater than the calculated oxygen atomic valence s-p separation while valence widths for the other anions closely match atomic valence s-p splittings. This effect arises from the instability of the peroxide antibonding orbitals which correlates with the absence of dsu n peroxides and Superoxides. Calculations on a Cin2 v geometry FeO 6su9− cluster show that the difference in energy of O2 p nonbonding and Fe3 d crystal field type orbitals drops sharply as an O-O edge is contracted, providing a mechanism for Fe 3+ → Fe 2+ reduction at high pressure.