Photoinduced Molecular Dynamics in Solution by Gianluca Levi

Author:Gianluca Levi
Language: eng
Format: epub
ISBN: 9783030286118
Publisher: Springer International Publishing

7.1 Pump-Probe Experiments at XFELs

Time-resolved structural determinations with X-rays are based on the pump-probe operative principle: an ultrashort optical pump laser initiates a reaction, which is probed, after a time delay , by an ultrashort X-ray pulse focused on the sample. By collecting and putting in a sequence scattering images acquired at different pump-probe time delays, it is possible to produce a “molecular movie” of the dynamics consisting of a series of “snapshots” of atomic motion, if the setup permits to achieve an adequate time resolution. The pump-probe experiments that we perform use a UV-vis ultrashort laser that triggers nuclear dynamics by electronically exciting solute molecules in dilute solution. The use of a UV-vis pump pulse implies that the processes that can be studied with this technique are photochemically activated reactions. However, one should not think that this confines the investigation to excited-state PESs. As we will see in the next section, a careful choice of pump-pulse parameters can enable direct probing of ground-state PESs as well.

Fig. 7.1Schematical illustration of an optical pump/X-ray probe setup for time-resolved X-ray diffuse scattering (XDS) experiments

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