Resonant Inelastic X-ray Scattering (RIXS) Studies in Chemistry: Present and Future

Abstract

This chapter illustrates how resonant inelastic x-ray scattering (RIXS) is used to address questions in chemistry, with special focus on the electronic structure and catalytic activity of first row transition metals. RIXS is a two-photon process that is the x-ray equivalent of resonance Raman spectroscopy. The final states correspond to vibrational, valence electronic or even core excitations. In addition to the advantages of a local element-selective x-ray spectroscopic probe, RIXS gives new information compared to single-photon x-ray absorption and x-ray emission experiments. Metal L-edge RIXS shows intense metal-centered ligand-field transitions, even in cases where they are spin or parity forbidden in optical absorption spectroscopy. By selecting different resonances by appropriately tuning the incident energy, it is possible to isolate different ligand-field and charge-transfer transitions. The observation of a large number of electronic states that can be properly assigned, sometimes with the help of theoretical methods, gives novel opportunities to quantify metal-ligand interactions and their contributions to reactivity. RIXS in the K pre-edge can be used to obtain L- and M-edge like spectra including insight into charge-transfer excitations all with the advantages of a hard x-ray probe. Finally, it is shown how time-resolved RIXS down to the femtosecond timescale probes the orbitals of transient reaction intermediates. The usefulness of RIXS in chemistry is shown for a diverse set of systems, including coordination complexes, metalloproteins, and nanoparticles.