| People involved: | Jens Uhlig, Sophie Canton, Villy Sundström |
| Former members: | Monika Walczak, Wilfred Fullagar, Robert Smith, Niklas Gador |
| Involved facilities: | Laser plasma source, Synchrotron facilities |
This technique has the following projects (and possibly other techniques) related to it:
What knowledge is needed to characterize function of a biomolecule, molecular material or a chemical reaction mechanism? Structure has long been considered to be the key information and several powerful techniques like X-ray crystallography and multidimensional NMR have been developed, following the notion that "seeing is believing", to provide equilibrium (static) structures of molecules. At the same time function of a molecular system implies change of structure and in order to characterize and understand how a biomolecule or material works it is necessary to know how and why the structural changes occur. The How is related to finding out precisely which structural changes occur, which atoms are involved, how are they affected, which bonds are broken, how does energy and charge flow through the molecule, and what are the temporal characteristics of the changes. The Why is associated with energetics and interactions; what is the energy landscape that connects reactants, intermediates and products and how do molecules interact with each other and with their environment? Ultimate understanding of a process enables the control of it. The wish to advance our understanding of molecular systems from equilibrium structures to function and eventually to enable reaction control, can be seen to require development of experimental techniques that resolve structural dynamics.
Distances between chemically bonded atoms are ~10-10 m. The wavelength of visible light (~10-6 m) is extremely large in comparison. When a visible light wave interacts with two bonded atoms, each atom sees approximately the same value of lights electrical field, so that light waves scattered from the two atoms have almost the same phase. The result is that scattered visible light cannot be directly used to determine the spatial relationship of two bonded atoms. This situation changes when the wavelength becomes similar to the distance between objects. In addition to X-rays, the de Broglie relationship between momentum and wavelength (p=h/λ) indicates that any moving particle has a corresponding wavelength. Electrons, neutrons, other subatomic particles and even entire molecules can be given a speed such that their de Broglie wavelength is approximately the distance between atoms. The nature of the particle-sample interaction differs in each case, but de Broglie wavelengths comparable to inter atomic distances can be exploited for chemical structure determination, this being the basis for electron and neutron structure techniques.
General overview and motivation for X-ray based measurements (This page)
X-ray absorption spectroscopy
X-ray Diffraction and the argumentation for broad bandwidth
Overview and motivation for ultrafast X-ray measurements
Developments done on ultrafast X-ray sources in Lund
Developments on X-ray Detectors
Measurements done on ultrafast synchrotron user facilities
Steady state measurements done on synchrotrons