PNNL

Abstract

We probe, at high energy resolution, the double electron excitation (KLII&II) x-ray absorption region that lies approximately 115 eV above the main Al K-edge (1566 eV) of a-alumina and sodium aluminate. The two solid standards, a-alumina (octahedral) and sodium aluminate (tetrahedral) are compared to aqueous species that have the same Al coordination symmetries, Al3+•6H2O (octahedral) and Al(OH)4- (tetrahedral). For the octahedral species, the edge height of the KLII&III-edge is approximately 10% of the main K-edge however the edge height is much weaker (3% of K-edge height) for Al species with tetrahedral symmetry. For the a-alumina and aqueous Al3+•6H2O the KLII&III spectra contain white line features and extended absorption fine structure (EXAFS) that mimics the K-edge spectra. The KLII&III-edge feature interferes with an important region of the extended-XAFS region of the spectra for the K-edge of the crystalline and aqueous standards. The K-edge spectra and K-edge positions are predicted using time-dependent density functional theory (TDDFT). The TDDFT calculations for the K-edge XANES spectra reproduce the observed transitions in the experimental spectra of the four Al species. The KLII&II and KLI onsets and their corresponding chemical shifts for the four standards are estimated using the delta self-consistent field (?SCF) method. Research by JLF, NG, EJB, AV, TDS was supported by U.S. Department of Energy’s (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. NG thanks Amity Andersen for help with the a-Al2O3 and tetrahedral sodium aluminate (NaAlO2) clusters. All the calculations were performed using the Molecular Science Computing Capability at EMSL, a national scientific user facility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated for DOE by Battelle under Contract # DE-AC05-76RLO-1830.