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== Pump-Probe Technique ==
TR-XSS is a pump-probe technique, in which the liquid sample is first excited with a short laser pulse and subsequently probed with a short X-ray pulse. The liquid sample contains low concentrations (~1-100 mM) of a solute molecule in solution, which is delivered to the beam interaction region either by a liquid jet or through a capillary. A continuous supply of new sample through the delivery system avoids radiation damage by the X-ray and laser pulses. The intensity I(θ) of the [[X-ray_diffraction|X-rays]] scattered on the sample is recorded as a function of the scattering angle θ with a two dimensional X-ray detector. The intensity distribution of scattered light contains information on all molecules in the liquid sample, including the target molecule for the investigation (solute) as well as the solvent molecules surrounding it ([[Solvation_shell|solvation shell]]) and all solvent molecules. To highlight the information gathered on the excited solute molecules, detector images with scattering patterns I(θ) from the sample in the [[Ground_state|ground state]] (I<sub>''laser off''</sub>) are subtracted from scattering pattern after [[Excited_state|exciting]] the solute with a pump laser (I<sub>''laser on''</sub>).
ΔI(θ,Δt) = I<sub>''laser off''</sub> (θ) – I<sub>''laser on''</sub>(θ,Δt) only contains intensity contributions from the excited solute and solvation shell molecules, which reacted to the chemical reaction triggered by == Application ==
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