A THEORETICAL-STUDY OF THE OXYGEN-K ABSORPTION-EDGE IN CLUSTER-MODELSOF SODALITE

The X-ray absorption near-edge spectrum (XANES) has been calculated fo r the oxygen K-edge in cluster models of pure silica sodalite and a re lated sodalite containing Al. Results are reported which describe the dependence of the calculated near-edge spectrum on cluster size as wel l as the presence of Al and the charge-balancing Na cations. Prominent features of the calculated spectra appear to be correlated with the u nderlying structure of the cluster models. In agreement with other cal culations and measurements of near-edge structure in oxides, backscatt ering of the outgoing photoelectron from 0 atom neighbors is the domin ant source of XANES structure, whereas backscattering from Si atoms ha s a relatively minor effect. Also calculated was the spectrum of a sma ll cluster model of alpha-SiO2, which compared favorably with a previo usly reported experimental near-edge spectrum.