Mapping the evolution of charge distributions, oxidation states, and frontier orbitals via time-resolved resonant inelastic X-ray scattering (RIXS) is a powerful approach providing element-specific insight to the dynamics of chemical bonds and excited-state charge distributions. Soft X-ray RIXS is particularly sensitive to the most abundant elements (C, N, O) that comprise ligand structures, and to the d-electrons of abundant transition metals.
The solvent environment plays a critical role in molecular charge-transfer reactions, but direct observation of the relevant short-range coupled solvent motions is a significant challenge. Multi-modal time-resolved X-ray scattering and spectroscopy reveal the correlated solvent and electronic structural dynamics associated with photo-induced metal-to-metal charge transfer in a mixed-valence complex.
Excited-state reaction pathways are mediated by close coupling of charge dynamics and subtle changes in atomic structure. Multi-modal time-resolved X-ray scattering and spectroscopy directly quantify the initial molecular excited-state coupling of electronic and structural configurations with atomic resolution and spin-state specificity.
Thermally-driven chemistry is mediated by the transition state that separates reactants from products, and determines reaction pathways. Understanding the chemical structure of ephemeral transition states is a grand challenge in chemistry. LCLS studies have directly observed transition states for the first time via element-specific time-resolved X-ray spectroscopy following the stimulation of catalytic CO oxidation on Ruthenium.