Water molecule movements help understand energy landscape

In Germany, for the first time, scientists from Ruhr University Bochum were able to fully observe all movements between water molecules, the so-called intermolecular vibrations. The findings help, among other things, to better determine the energy landscape of the molecules and thus to better understand the strange properties of water.

Of particular importance is a certain movement of individual water molecules against each other, the so-called hindered rotation movement.

Water is the most important solvent in chemistry and biology and has a number of strange properties – for example that it reaches its greatest density at four degrees Celsius. The special interactions between the water molecules are responsible for this. “Describing these interactions has been a challenge for research for decades,” says Martina Havenith, head of the Bochum Chair for Physical Chemistry II and spokeswoman for the Ruhr Explores Solvation ( Resolv ) cluster of excellence .

The team investigated the simplest possible interaction, namely between exactly two individual water molecules, using terahertz spectroscopy.

With this experimental setup, the group was able for the first time to record a spectrum of the hindered rotational movement of two water molecules. “Water molecules are constantly moving,” explains Martina Havenith. “They turn, open and close.” However, a water molecule that has a second water molecule in its vicinity cannot rotate freely – this is why it is called a blocked rotation movement.