Nonresonant Inelastic X-ray Scattering and X-ray Raman Scattering

Abstract

In analogy to the connections between Raman scattering and absorption in the optical regime, X-ray Raman scattering (XRS) is an alternative to X-ray absorption spectroscopy, particularly for sub-keV excitations. XRS is the nonresonant inelastic X-ray scattering (NIXS, or NRIXS) from core or semi-core electrons and has a similar energy-dependence as X-ray absorption, albeit with a much smaller overall cross section. However, as a high-energy photon-in/photon-out approach, XRS has found widespread use for samples at extreme conditions, such as high pressure experiments in diamond anvil cells, as well as samples incompatible with vacuum conditions, like many liquids. Compared to absorption spectroscopy, XRS has key technical advantages beyond bulk sensitivity, including lack of self-absorption and the ability to access dipole-forbidden final states in certain cases. It also shares many of the same components as hard X-ray absorption/emission spectroscopy and has found a niche as a complementary technique available at multiple synchrotron facilities worldwide [1–9].