Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics

Ultrafast electronic and structural dynamics ofmatter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functionalmaterials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital andmagnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited statemoieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital andmagnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)5 in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics withAS-RXRSwith transform-limited x-ray pulses is given—whichwill be covered experimentally by upcoming transform-limited x-ray sources. With the rapid evolution of sub-picosecond and femtosecond x-ray sources and particularly with the emergence x-ray free-electron lasers, first steps to join the unique electronic structure information of x-ray spectroscopy with the ultrafast time scale of dynamics inmatter have been taken [1–8]. Often though, time resolved x-ray spectroscopy at these dilute transient species with x-ray absorption, x-rayfluorescence or electron spectroscopy suffer often from the difficult separation between the overlapping spectral signatures of the dilute excited state species and the ground state. To reach improved chemical selectivity with x-ray lasers nonlinear and OPEN ACCESS