Influence of Förster-type energy transfer on the vibrational relaxation of anionic hydration shells.

We study the influence of Förster energy transfer on the vibrational relaxation dynamics of anionic hydration shells by performing time-resolved mid-infrared spectroscopy on the OH-stretch vibration of water molecules in aqueous solutions of sodium iodide. We observe that the Förster energy transfer leads to a pronounced acceleration of the vibrational relaxation. We describe the observed dynamics with a model in which we include the Förster vibrational energy transfer between the different hydroxyl groups in solution. With this model we can quantitatively describe the experimental data over a wide range of isotopic compositions and salt concentrations. Our results show that resonant energy transfer is an efficient mechanism assisting in the vibrational relaxation of anionic hydration shells.