X-ray Lasers Create New Opportunities in Chemical Physics

I will present two examples of how x-ray lasers can be used to probe fundamental problems in chemical physics with a focus on recent results from LCLS.
Catalysis is central for many chemical energy transformations that occur at interfaces. One of the dreams is to follow catalytic reactions in real time from reactants over various intermediates to products. The prospective for the study of chemical reactions on surfaces using x-ray free-electron lasers with femtosecond time resolution will be presented together with the first results of CO desorption and CO oxidation.

Water is the key compound for our existence on this planet and it is involved in many important physical, chemical, biological and geological processes. Although water is the most common molecular substance it is also most unusual with many anomalies in its thermodynamic properties such as compressibility, density variation and heat capacity. The deviation of these properties is strongly enhanced upon supercooling water below the freezing point. Here, we demonstrate a new, general experimental approach to study the structure of liquid states at supercooled conditions below their limit of homogeneous nucleation. We use femtosecond x-ray pulses generated by the LCLS x-ray laser to probe evaporatively cooled droplets of supercooled bulk water and find unambiguous experimental evidence for the existence of metastable bulk liquid water down to temperatures of 227 K in the previously largely unexplored “no-man’s land”.