Guest-Host Interactions

Guest-host interactions between reacting molecules and their local solvent environment have been pursued ever since the expression “cage effect” was coined by Frank and Rabinowitch in 1934. The cage effect mainly describes the difference in reaction outcome when comparing gas phase reactions to those in liquid environments. This was studied with the advent of femtosecond laser systems since the 1980s, which observed different time scales for the ongoing solute reaction as a function of the selected solvent. However, a real-time imaging of these processes on the atomic scale and with the required femtosecond time-resolution remained out of reach.

We investigate solvation dynamics including guest-host interactions with a suite of structurally sensitive x-ray tools, and this with femtosecond time resolution. One goal is to add a new observable, namely to possibly image the ongoing reaction involving one solute molecule together with its surrounding host molecules. Wide Angle X-ray Scattering (WAXS) of disordered liquids can provide some structural information, while Extended X-ray Absorption Fine Structure tools (EXAFS) can measure the distance from a key atom in the reacting solute to its nearest neighbor solvent molecules. X-ray Absorption Near-Edge Structure (XANES) and X-ray Emission Spectroscopy (XES) are additional tools delivering electronic structure information within the reacting solute molecule.

In short, we aim to reveal the dynamics of both constituents, solvent and solute, which occur on comparable femtosecond time scales. We aim to reveal this way more details about the elementary steps of chemical reactions in condensed phase media.