High resolution 1s core hole X-ray spectroscopy in 3d transition metal complexes—electronic and structural information

The creation of a 1s core hole in a 3d transition metal ion gives rise to an emission spectrum that can be recorded using a crystal analyzer. K shell X-ray spectroscopy using an analyser energy bandwidth of ∼1 eV is sensitive to electron–electron interactions and orbital splittings and preserves the advantages of the hard X-ray probe. We review recent developments in Kα and Kβ spectroscopy and show how the chemical sensitivity of the fluorescence lines can be exploited for selective X-ray absorption studies. When the photo excitation energy is tuned close to the K edge threshold, the phenomenon known as X-ray resonant Raman or resonant inelastic X-ray scattering (RIXS) occurs. RIXS spectroscopy on 3d transition metals at the 1s resonances with lowest incident energies (K pre-edge) is a very recent technique. We discuss basic aspects and demonstrate with several examples its potential as a future routine spectroscopic tool.