Resonant Raman Scattering. A New tool for oxidation State Determinations

J. J. LEANI; H. J. SÁNCHEZ; M.C. VALENTINUZZI; C. A. PÉREZ

Coimbra

Conferencia; EXRS 2010; 2010

X ray fluorescence spectra present singular characteristics produced by the different scattering processes. When atoms are irradiated with incident energy lower and close to an absorption edge, scattering peaks appear due to an inelastic process known as Resonant Inelastic X ray Scattering (RIXS) or Resonant Raman Scattering (RRS). In this process, the emitted photons have a continuous energy distribution with a high energy cut-off limit. In the last few years experiments of RRS has become a very powerful technique to investigate excitations of electrons in solids [1,2].   This work presents the first results regarding the possibility of determining the oxidation state by RRS spectroscopy using an energy-dispersive system combined with synchrotron radiation. Pure samples of transition metals (Cu, Fe, Mn) and different oxides of them (CuO, Cu2O, Fe2O3, Mn2O3) were irradiated using monochromatic synchrotron radiation at the XRF station of the D09B-XRF beamline [3] at the Brazilian synchrotron facility (LNLS, Campinas) [4], below and close to their absorption edges to inspect the RRS emissions.   The spectra were analyzed with specific programs for fitting the experimental data to theoretical expressions. After that, residuals were determined in the low energy side of the RRS peaks and a Fast Fourier Transform (FFT) smoothing procedure was applied, taking into account the instrument functions of the detecting system. The results show an oscillation pattern that depends on the sample, i.e. on the oxidation state. These changes in the RRS structure between the pure elements and their oxides are discriminated and suggest the possibility of structural characterization by means of resonant Raman scattering using an energy-dispersive system combined with synchrotron radiation.     More measurements in different absorbing elements and oxidation states are currently carried out in order to verify the present results and to establish a repetitive and reliable method of structural determination.   References 1.   K. Ishii, et al, Phys. Rev. Lett. 94, 207003 (2005). 2.   A. Kotani y S. Shin, Rev. Mod. Phys. 73, 203 (2001). 3.  C.A. Pérez, et al, X Ray Spectrom; v. 28 pp. 320-326 (1999). 4.  A.R.D. Rodríguez, et al. Proceedings of the Particle Accelerator Conference - PAC97, Vancouver (1997).