Pump-probe experiments and time-resolved diffraction

Researchers are able to track ultra-fast changes in atomic and molecular structures by first triggering the change with a laser (pump) and then analysing it with an X-ray beam (probe) after a given time. Future dedicated beamlines will be able to watch chemical reactions, such as the splitting of water into hydrogen and oxygen, as they happen on a timescale of less than a billionth of a second. 

The figure below shows a snapshot of myoglobin MbCO taken 100 picoseconds after the dissociation of CO was triggered by a flash of light from a femtosecond laser. Blue and red colours show regions where the protein gained or lost electron density. By recording Laue images as a function of the delay from the laser flash, the change in the electron density is mapped as a function of time (F. Schotte et al., Science 300, 1944-1947 (2003)). The Upgrade will permit similar experiments to be envisaged with larger and more complex proteins, over a broader range of techniques.

Example: A time-resolved experiment can be used to study interactions between atoms within a protein and a substrate.

Experiments on reaction dynamics

Two beamlines employing high-energy X-ray beams will allow ultra-rapid changes in the electronic structure of atoms to be followed in real time by first exciting the sample with a very short laser pulse and then carrying out diffraction and spectroscopy measurements (pump and probe). Such studies are essential in the development of materials for solar cells, for example. One significant aim is to extend the pump-and-probe approach to biological molecules and assemblies involved in energy production in their natural watery environment.

Applications

• Industrial chemical reactions
• Solar energy
• Hydrogen fuel storage
• Protein dynamics
• Biological processes such as photosynthesis
• Chemistry of climate change

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