The barium giant dipole resonance in barite: a study of soft X-ray absorption edges using hard X-rays

Abstract

Giant dipole resonances are collective phenomena which can be found in systems ranging from atoms through clusters to solids. In atomic and solid state physics such excitations are usually studied by soft X-ray absorption, photoelectron and electron energy-loss spectroscopies. With the advent of thirdgeneration synchrotron radiation sources, nonresonant inelastic X-ray scattering became a prominent tool to study truly bulk sensitive shallow absorption edges with high energy photons. The method is not limited to measuring dipole transitions but allows the study of final states of different symmetry due to monopole and quadrupole transitions employing its momentum-transfer dependence. In this paper the potential of nonresonant inelastic X-ray scattering to probe low-energy excitations is emphasized with the focus on symmetry selectivity, study of liquids and high pressure applications. As an example, nonresonant inelastic X-ray scattering spectra of the barium 4d-f giant dipole resonance in barite are discussed.

The Ba 4d–4f giant dipole resonance in complex Ba/Si compounds

“…[34]. The preedge features between 90-101 eV energy loss, most prominently observed for BaSO 4 , are predominantly due to non dipole allowed multiplet transitions and thus gain significant spectral weight for large momentum transfers.…”

“…However, the second maximum around 119 eV is strongly suppressed in the calculated spectra of all materials as compared to the experimental findings. It has been discussed earlier that besides a possible dipole resonance modulation predicted by Wendin [14], double ionization processes [45] might contribute to the spectrum in the energy loss range between 111 and 130 eV [34] and that such double electron excitations can obscure the GR's shape. [4,46,11] Double ionization processes are not accounted for in the theoretical approach.…”

“…Refs. [12,34,44] for details). To simulate the spectra of the investigated compounds, the Ba N IV,V absorption edge spectra were calculated for each non-equivalent atom in the unit cell and the resulting spectra were added up accounting for the corresponding multiplicities.…”

High-resolution nonresonant x-ray Raman scattering study on rare earth phosphate nanoparticles

“…They correspond to nondipolar (high-order multipole) excitations that have been also observed in electron energy loss spectroscopy (EELS) [11]. More recently, their existence was also reported in XRS [12,13]. Gordon et al [14] studied them in detail and noted that their contribution became dominant in the XRS spectra of LaPO 4 and CePO 4 at large exchanged momenta.…”

“…The dipolar spectrum for La was modeled using the real space multiple scattering (RSMS) approach, using the FEFF code [33] within the time-dependent local density approximation (TDLDA) to account for collective phenomena. This method has worked well for barite (BaSO 4 ) [13] and for complex Ba/Si compounds [4].…”