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Ultrafast single-particle imaging with intense x-ray pulses from free-electron laser sources provides a new approach for visualizing structure and dynamics on the nanoscale. After a short introduction to the novel free-electron laser sources and methods, we highlight selected applications and discuss how ultrafast imaging flourishes from method development to early applications in physics and biology to opportunities for chemical sciences.

X-ray techniques have long been applied to chemical research, ranging from powder diffraction tools to analyse material structure to X-ray fluorescence measurements for sample composition. The development of high-brightness, accelerator-based X-ray sources has allowed chemists to use similar techniques but on more demanding samples and using more photon-hungry methods. X-ray Free Electron Lasers (XFELs) are the latest in the development of these large-scale user facilities, opening up new avenues of research and the possibility of more advanced applications for a range of research. The SwissFEL XFEL project at the Paul Scherrer Institute will begin user operation in the hard X-ray (2.1–12.4 keV) photon energy range in 2018 with soft X-ray (240–1930 eV) user operation to follow and here we will present the details of this project, it's operating capabilities, and some aspects of the experimental stations that will be particularly attractive for chemistry research. SwissFEL is a revolutionary new machine that will complement and extend the time-resolved chemistry efforts in the Swiss research community.

Understanding the role of peroxides in combustion, in atmospheric and in surface science involves investigations on a molecular level, at which energy transfers and rearrangements of the nuclei dictate the chemistry. Due to their high reactivity they appear as unstable transient species, which impedes detailed spectroscopic investigations. Low frequency modes, especially internal and hindered rotations with energies less than 200 cm-1 play an important role for the determination of molecular energies and reaction rates. Unfortunately, these motions are in general difficult to address. Femtosecond four-wave mixing (fs-FWM) is a powerful tool that allows for investigations of ground state dynamics of molecules. The high peak-power output of fs-lasers, facilitates the excitation of weak Raman coherences. Results from the combustion relevant di-tert-butyl peroxide molecule are exemplified.