MULTIPLE-SCATTERING ANALYSIS OF NEXAFS SPECTRA OF MOLECULAR-OXYGEN ANIONS IN DIFFERENTLY GROWN CESIUM OXIDES

Different cesium oxides have been prepared in situ and studied by near -edge x-ray-absorption fine structure (NEXAFS) measurements. The data have been analyzed by multiple-scattering calculations for two model s tructures, CsO2 and Cs2O2 using self-consistent final-state potentials . The analysis shows that the sample grown by codeposition of oxygen a nd cesium has Cs+O2- structure with an O-O distance in the molecular a nion of 1.40 +/- 0.05 angstrom, whereas the sample obtained on oxidizi ng a thin Cs film has Cs2+ O2(2-) structure with an O-O distance of 1. 55 +/- 0.05 angstrom. Both distances are larger than the values for th e 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 O2(2-) anio n are sensitive to its surrounding matrix.