Ultrafast solvation dynamics around aqueous halides

Solvent plays an important role in the stability, assembly and proper functioning of biochemical molecules. Small changes in the solvent parameters can make or break the biochemistry of the said molecules. Upon photoionization of a solute molecule the surrounding solvent molecules respond by rearranging to this change of charge distribution. Solvation Dynamics around molecules is very complex and is described by Dynamics Stokes Shift. Our approach utilizes mono-atomic halide (X) solutes which exhibit no internal degrees of freedom. This way one can extract solvation dynamics in its purest form. Previous studies focused on observing the solvated electron via Transient Absorption Spectroscopy. Its absorption band rapidly blue-shifts. The electron survival kinetics exhibits a roughly 10 ps initial decay followed by a flattening on the nanosecond time scale. The initial decay is attributed to the existence of a so called Contact Pair (X:e), which should exhibit the same absorption spectrum as the solvated electron itself. With X-Ray Absorption Spectroscopy we can observe the electronic structure changes of the ionized atom. In order to directly observe spatial structure changes X-Ray diffraction methods are useful. Combining X-ray absorption with transient optical absorption spectroscopies we can monitor the atom-electron recombination both from the viewpoint of the nascent atom (x-rays) and from the solvated electron. We can also monitor the appearance of dihalides (via X + X- → X2-) on the same time scales. With these observables we can track the entire kinetic sequence and deliver a new understanding of the ensuing kinetics and dynamics, especially concerning the existence of the contact pair.