For high resolution X-Ray Adsorption Spectroscopy, XAS, described as HR-XANES, the XAS is taken as a slice of the Resonant Inelastic X-Ray Scattering, RIXS map; see, for example, Refs. [1-2]. There is, however, the concern that the RIXS slice may contain features not present in the direct excitation to the core-excited states as modeled with XAS. This is because there are overlaps between different portions of the RIXS features due to the broadening of the RIXS measurements.3 In this work, we make a direct comparison of slices of theoretically generated RIXS maps with the direct theoretical XAS calculations. The wavefunctions for the initial, intermediate, and final states where the core-hole is filled are obtained as fully relativistic ab initio solutions of Dirac Hartree-Fock and many body configuration interaction solutions.4 The intensities for the XAS and the RIXS spectra are computed from many-body dipole matrix elements between the initial and intermediate, for XAS and RIXS, and the intermediate to final. for RIXS. This is the first time that such a direct comparison, with the same level of theoretical treatment for the XAS and RIXS has been made. The comparison will be made for selected edges of Neptunyl compounds.

Comparison of RIXS cuts and direct XAS excitations

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