The XPS spectra of cerium compounds containing oxygen

The fine structure of XPS lines of electrons of valent and inner subshells in cerium oxide CeO2, orthoniobate CeNbO4, ortomethoxibenzoate CeL3(L = C6H4OCH3COOH-) and diphenylacetate CeL3'. 2H(2)O(L' = (C6H5)(2)CHCOO-) was studied in the range of electron binding energies from 0 up to 1350 eV. Its comparison with trifluoride CeF was carried out in order to determine the mechanism of such structure occurrence and the oxidation degree of cerium ions in the compounds. It was established that the structure Ce(III) has more in common with the studied compounds and differs essentially from that of the Ce(IV) in cerium oxide CeO2. It allows one to determine the oxidation degree of the cerium in the compounds on the basis of the values of the XPS line parameters. On the basis of experimental data it was supposed that the structure, for example of the Ce3d-electron spectrum in CeO2, is connected with final electronic states of cerium ion: Ce3d(9)4f(0), Ce3d(9)4f(1)VMO(-1) and Ce3d(9)5s(1)(5p(5))4f(0)ns(np). It is worth noting that the unique final state formally designated as Ce3d(9)5s(1)(5p(5))4f(0)ns(np) is not the state with the additional hole on the atomic Ce5s(5p) orbital, bur that of on inner valent molecular orbital of a(1g) (t(1u)) type for the cluster CeO812- of O-h symmetry group, generally consisting of Ce5s(5p), O2s and O2p atomic orbitals of neighbouring Ce and O atoms in CeO2. (C) 1998 Elsevier Science B.V.