Multiple-scattering analysis of NEXAFS spectra of molecular oxygen anions in differently grown cesium oxides.

Abstract

Different cesium oxides have been prepared in situ and studied by near-edge x-ray-absoprtion fine structure (NEXAFS) measurements. The data have been analyzed by multiple-scattering calculations for two model structures, ${\mathrm{CsO}}_{2}$ and ${\mathrm{Cs}}_{2}$${\mathrm{O}}_{2}$ using self-consistent final-state potentials. The analysis shows that the sample grown by codeposition of oxygen and cesium has ${\mathrm{Cs}}^{+}$${\mathrm{O}}_{2}^{\mathrm{\ensuremath{-}}}$ structure with an O-O distance in the molecular anion of 1.40\ifmmode\pm\else\textpm\fi{}0.05 \AA{}, whereas the sample obtained on oxidizing a thin Cs film has ${\mathrm{Cs}}^{2+}$${\mathrm{O}}_{2}^{2\mathrm{\ensuremath{-}}}$ structure with an O-O distance of 1.55\ifmmode\pm\else\textpm\fi{}0.05 \AA{}. Both distances are larger than the values for the corresponding free ions. Models assuming charge transfer between the alkali and oxygen atoms other than quoted above can be excluded. The analysis also shows that the localized empty states of the ${\mathrm{O}}_{2}^{2\mathrm{\ensuremath{-}}}$ anion are sensitive to its surrounding matrix.