title: Electronic and Chemical State of Aluminum from the Single- (K) and Double-Electron Excitation (KLII&III, KLI) X-ray Absorption Near-Edge Spectra of α-Alumina, Sodium Aluminate, Aqueous Al(3+)·(H2O)6, and Aqueous Al(OH)4(-).
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 α-alumina and sodium aluminate. The two solid standards, α-alumina (octahedral) and sodium aluminate (tetrahedral), are compared to aqueous species that have the same Al coordination symmetries, Al(3+)·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 α-alumina and aqueous Al(3+)·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 in the EXAFS spectra of the crystalline and aqueous standards. The K-edge spectra and K-edge energy positions are predicted using time-dependent density functional theory (TDDFT). The TDDFT calculations for the K-edge X-ray absorption near-edge spectra (XANES) 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 (ΔSCF) method.
authors.forename: John L
authors.initials: JL
authors.lastname: Fulton
authors.forename: Niranjan
authors.initials: N
authors.lastname: Govind
authors.affiliation: ⊥Swiss Light Source, Laboratory for Catalysis and Sustainable Chemistry (LSK), Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Huthwelker
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Bylaska
authors.forename: Aleksei
authors.initials: A
authors.lastname: Vjunov
authors.affiliation: ⊥Swiss Light Source, Laboratory for Catalysis and Sustainable Chemistry (LSK), Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland.
authors.forename: Sonia
authors.initials: S
authors.lastname: Pin
authors.forename: Tricia D
authors.initials: TD
authors.lastname: Smurthwaite