Watching the dance of ions and molecules in the THz

Ion hydration is a fundamental question in chemistry with many implications for biology -ranging from ion transport in membrane channels to ion transports in electrolytes. The discussion about the solvation mechanism of different salts has been initiated over a century ago by introduction of the Hofmeister series; however the molecular picture of ion hydration is still part of a controversial scientific debate. By using the sensitivity of THz absorption spectroscopy to detect solute-induced changes in the low-frequency spectral range and combining these with MD simulations we are now able to provide a detailed molecular picture of the hydration of cations and anions and watch their motions.