New applications ofq-dependent XRS across the periodic table

Abstract

C157Microsymposia XRS has long been discussed in an important but somewhat limited context, specifically, as a bulk-sensitive alternative to x-ray absorption spectroscopies. However, continuing developments in both experimental apparatus and theoretical methods are steadily opening up new opportunities which are special to the large momentum transfers q which can be accessed in XRS. In this presentation, we will survey a few such recent studies. These will include applications for basic spectroscopy (He gas), environmental and renewable energy (N2 gas and LiTiOx), exotic chemical bonding (C2B10H12), and f-electron physics (CeO2 and UO2).Keywords: inelastic x-ray scattering, X-ray Raman scattering, electron energy loss spectroscopy MS.94.4Acta Cryst. (2008). A64, C158 X-ray Raman of water in the condensed phasesJohn S Tse University of Saskatchewan, Physics and Engineering Physics, 116 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada, E-mail John. Tse@usask.caIn-situ measurement of the x-ray Raman spectra on the oxygen K-edge of several forms of ordered and disordered ice will be reported. It is shown there is a significant difference in the absorption profile in the near-edge and post-edge region between crystalline and amorphous ices. Comparisons between observed and theoretical spectra are made. Difficulties in the first-principles calculation of core level absorption spectra will be discussed.Keywords: X-ray raman, a ray absorption spectroscopy, ice MS.94.5 Acta Cryst. (2008). A64, C158High-resolution X-ray Raman scattering and the study of ices under high pressure Yong CaiBrookhaven National Laboratory, National Synchrotron Light Source II, Bldg 817, Upton, New York, 11973-5000, USA, E-mail cai@bnl.gov High-resolution x-ray Raman scattering (XRS) of oxygen K-edge in various forms of ices have drawn a great deal of interest recently. The double differential cross section can be shown to provide the same information as that obtained by x-ray absorption spectroscopy (XAS) when the momentum transfer is small enough that the dipole approximation is valid. For low-Z elements whose inner shells are in the soft x-ray region, XRS possesses unique advantages compared to XAS due to its inherent bulk sensitivity and good penetration depth, and is especially valuable for studies under extreme thermodynamic conditions such as high pressure. At a total energy resolution of ~300 meV at 9.89keV, studies on ices III, II, IX, VI and VII at various pressure and temperature conditions indicate that the technique provides clear spectral sensitivity to both short-and long-range structural changes of the H2O frame work. Our studies, for example, have revealed that a diminishing intensity of the pre-edge feature provides a clear signature of proton ordering in the H2O frame work [1]. The technique, when coupled with optical Raman and x-ray diffraction, provides also a powerful tool for understanding the chemistry in the disassociation of H2O induced by the incident x-rays under certain (P, T) conditions [2,3]. Details of thes...