II. Catalysis and Solution Chemistry

Structure and lifetime of short-lived molecular states in solution or on a catalytic surface

  • Chemical time scales
  • X-ray probes of chemical dynamics
  • CO chemistry on Ru (001): thermal vs. electronic excitation
  • The high- and low-spin states of [FeII(bpy)3]2+
In order to obtain a complete microscopic understanding of a chemical process, whether it be synthetic, catalytic, or biochemical, one needs to identify the geometrical and electronic structures of the shor t-lived molecular intermediate states involved and to determine the rates of transition between them. This deeper understanding will lead to the ability to manipulate these reactions, allowing us to control and enhance them to suit our purposes. Since molecular vibrations can lead to the breaking and reforming of chemical bonds, the vibrational period represents a fundamental time-scale for chemical processes. For example, the C=C bond of an ethene molecule acts as a spring, and the characteristic stretch vibrational mode of the resulting harmonic oscillator has a period of 19 fs. With its nm spatial and fs temporal resolution, the SwissFEL is a unique tool for the investigation of chemical states on this time scale: The scattering of hard X-rays and photoelectrons from the atoms of the molecule provides a detailed geometrical structure, and the energydependent X-ray absorption and emission spectra reveal details of the electronic orbitals involved. This interplay between electron orbitals and geometric structure is at the ver y hear t of chemistry, as it is the energy and shape of a molecule which determine its reactivity. The SwissFEL will allow us to visualize chemistry with unprecedented accuracy, permitting us to construct a molecular movie of reactions as they take place.