Wernet, Ph. FRA03 2015 2015-12 Photochemically activated molecules catalyze chemical reactions, but a molecular-level understanding of how these short-lived and reactive intermediates catalyze reactions has remained elusive. I will discuss how time-resolved soft x-ray spectroscopy at free-electron lasers enables a fundamental understanding of local atomic and intermolecular interactions and their dynamics b on atomic length and time scales of Ångströms and femtoseconds[1]. In a recent application[2], we used femtosecond resonant inelastic x-ray scattering (RIXS) at the LINAC Coherent Light Source (LCLS, Stanford, USA)[3] to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 in solution. This highlights the ability of femtosecond soft x-ray spectroscopy at free-electron lasers to probe frontier-orbital interactions with atom specificity. I will end by discussing how the currently available methodology can be extended towards probing complex biomolecules in physiological conditions[4]. I will show how in particular high-repetition rate x-ray free-electron laser sources such as the planned LCLS-II will enable probing the local chemistry and it dynamical evolution in metalloproteins.