REALISTIC CLUSTER APPROACH FOR INTERPRETING THE VALENCE-BAND STRUCTURE OF PHOSPHORUS OXYANIONS

The electronic structures of different phosphates were studied by usin g the DV-X alpha cluster molecular orbital method, Experimental data o n crystal structures from x-ray diffraction measurements were used to set up realistic model clusters. Theoretical XPS valence band spectra obtained from the DV-X alpha calculations were compared to our high-re solution XPS measurements on polycrystalline powder Li3PO4, Na3PO4, Na 4P2O7 and (NaPO3)(n) samples, These new measurements made possible a m ore rigorous test of the theoretical approach and more reliable shape analysis than the previous set of data obtained by non-monochromatized measurements combined with the resolution enhancement technique, Syst ematic study of different clusters showed that the cations around the PO4 cluster and the distortion of the PO4 tetrahedra due to the anisot ropic crystal forces play only a minor role and their influence on the valence band spectra was found to be negligible, In the case of polyp hosphates, considerable changes were found in the valence band spectra as a consequence of small changes in the bond angle of the P-O-P brid ges, Our results, based on cluster parameters specific to the anhydrou s crystals, are in good agreement with the experiments.