What squeezes atoms
Longuet-Higgins Young Author's Prize for RUB researcher
A glimpse into the world of the smallest particles
Why quantum particles are uncertain
At the extremely low temperatures, which are characteristic for superfluid helium, the researcher analysed quantum effects that lie far beyond our everyday perception: the Heisenberg uncertainty principle, which is the hallmark of quantum physics, is the reason why the location of quantum particles cannot be exactly determined. It is uncertain; scientists refer to it as “delocalised”. This effect can be described with an effective size of the nucleus, and it is stronger the lower the temperature and the lighter the nucleus. On the other hand, inter-atomic interactions, which make molecules out of individual atoms, counteract such a delocalisation. “They squeeze the nuclei, so to speak, and thus reduce uncertainty,” explains Łukasz Walewski. These two competing tendencies result in an entirely unexpected behaviour of hydrogen nuclei at ultralow temperatures when they are involved in hydrogen bonds.
Computer simulations with surprising result
Using computer simulations, Łukasz Walewski has found out that these hydrogen nuclei are extremely strongly localised at superfluid helium temperatures (approx. 1 K, i.e. minus 272 °C) due to the interactions with the neighbouring atoms. The effective size of a hydrogen nucleus is reduced to such a degree that it becomes even smaller than the effective size of much heavier chlorine or oxygen atoms. These should, according to superficial consideration, be more strongly localised than hydrogen nuclei, as it is known from higher temperatures. This mechanism could have consequences: “As one can imagine the effective size of atoms and atomic nuclei plays a crucial role in the formation of molecular bonds,” explains Łukasz Walewski. “It is particularly relevant in the structure of hydrogen bonds, because they do not only make water liquid, but also keep DNA together and are important for the folding of proteins.”
Learning to better understand experimental observations
The effect described above could be important for understanding the results from experiments: using “helium nanodroplet isolation spectroscopy” (HENDI) researchers measure highly precise vibrational spectra of molecules that are enclosed in water droplets in superfluid helium. Here, the following questions arise: which role do the interactions of hydrogen bonds with the surrounding helium play and how do they influence the superfluidity of the helium environment?
Cluster of Excellence “RESOLV”
The impact of microsolvation on small molecules in the gas phase and in helium droplets is studied by RUB researchers in the Cluster of Excellence “Ruhr Explores Solvation” RESOLV (EXC 1069), which was approved by the German Research Foundation in June 2012.
CV Łukasz Walewski
Łukasz Walewski was born in Warsaw in 1976 and finished his degree in physics in the same city. After completing his PhD degree, he started to work at the Chair of Theoretical Chemistry (Professor Dominik Marx). Here, he studies chemical reactions in superfluid helium by means of computer simulations.
Ł. Walewski, H. Forbert and D. Marx, Interaction-Induced Localization of Protons in Hydrogen Bonds at Superfluid Helium Temperatures. Mol. Phys. 2013, 111, 2555–2569