Femtosecond Soft X-ray Absorption Spectroscopy of Solvated Molecules

"Time-resolved laser spectroscopy and established x-ray methods have recently been combined to probe the local electronic and molecular structure with femtosecond x-ray pulses in time and energy. In the soft x-ray range, core-level transition are particularly sensitive to valence-charge distributions and to chemical coordination of and structure around lighter elements (C, N, O etc.) that are biologically relevant, holding tremendous potential for following chemical bonding and the formation of new molecular species in real time. This is particularly powerful for understanding molecular dynamics in solution, where important chemistry occurs. We study the ultrafast spin cross-over reaction in a solvated iron(II) complex by femtosecond soft x-ray spectroscopy of the iron L-edges. Our recent results in combination with charge transfer multiplet calculations reveal a wealth of information on the changes of the electronic valence charge distributions, including changes in ligand-field splitting, orbital delocalization and population, and the influence of ligand π-backbonding on ultrafast timescales. "