Theory of orientation-sensitive near-edge fine-structure core-level spectroscopy

We derive an expression for the double differential scattering cross sectio n for inner-shell excitation of atoms by fast electrons. Using the augmente d plane-waves approach for description of the photo electron, we find the i nelastic scattering cross section to be a function of energy loss and momen tum transfer, which is a priori not proportional to the local symmetry-proj ected unoccupied density of states. We show the importance of symmetries an d choice of coordinate systems, which may necessitate the consideration of cross terms in the expression for the inelastic scattering cross section, c oupling different angular momenta of the final state. This has important co nsequences for the interpretation of energy loss near-edge structure and it s counterpart x-ray absorption near edge structure. [S0163-1829(99)00820-6] .