Chemical enviroment induced changes in Kbeta emission spectrum of Cr

G. TIRAO; M TORRES DELUIGI; G. STUTZ; J.A. RIVEROS

Campinas

Congreso; XVI Reunión Anual de Usuarios del LNLS; 2006

LNLS

Making use of the versatility of an X-ray spectrometer, originally conceived for inelastic X-ray scattering experiments [1], and profiting by the high resolutionprovided by a backdiffracting crystal analyzer, Kb spectrum (Kb1;3, Kb2;5 andKb") and absorption edge in Cr metal and various Cr compounds was measuredat the D12A-XRD1 beamline. The instrumental resolution at the Cr Kb1;3 energywas calculated to be 1.5 eV. This improved energy resolution, as compared to thatof a commercial X-ray spectrometer, allowed chemical effect-induced enhancementand shift of emission lines to be examined with high accuracy. Linewidth and lineshift was investigated in Cr compounds exhibiting different oxidation state (Cr0,CrIII, CrVI).The influence of the oxidation state on the peak position as well as on thelinewidth could be clearly seen. For CrVI-compounds the Kb1;3-line shifts, relatedto Cr0, about 0.5 eV to lower energies, whereas for CrIII-compounds the line shiftsabout 1 eV to higher energies, contrarily to the results reported by Gamblin andUrch [2] (shift to lower energies for all oxidation state), and in accordance withlower resolution measurements of Iihara et al. [3]. Concerning the position of theKb2;5-line the opposite behavior was observed. The shift of the Kb" satellite linerespect to Kb2;5 was about 16 eV in all compounds, which is in accordance withthe type of ligand atom (oxygen).In XANES the valence state of the selected type of the atom in the sample andthe local symmetry of its unoccupied orbitals can be deduced from the informationhidden in the shape and energy shift of the x-ray absorption edge itself. The result-ing structure within about 30 eV of the threshold is rich in chemical and structuralinformation. The shape and position of the edge and the pre-edge resonances al-lowed information about the local symmetry of the investigated compounds to beobtained.