Research group Experimental X-ray studies of Liquids and Surfaces (XSoLaS)

Researchers at Stockholm University have developed a novel approach to examine chemical reactions and have applied it to the reduction of carbon monoxide by copper, a crucial step in the conversion of carbon dioxide into fuels. The results have recently been published in the journal Angewandte Chemie.

The UN General Assembly started the initiative in 1992 and since then, different water-related themes have been highlighted every year. In Sweden, World Water Day is coordinated by the Swedish Hydrological Council (SHR) and has been celebrated since 2006. At Fysikum, we tell you about our research on water during this day. This year's theme is water cooperation, for peace and security in its broadest sense. World Water Week will take place in Stockholm on August 24-25, 2024, when the winner of the Stockholm Water Prize will be announced.   Water research at Fysikum The Division of Chemical Physics hosts the research group XSOLAS, which stands for Experimental X-ray studies of liquids and surfaces (XSoLaS). The group focuses on the structure, dynamics and physical properties of water and water solutions. One of the research projects is Water, Ice and Water Solutions. - It has been known for several decades that many of the properties of water, such as density, compressibility and heat capacity, become strongly deviated when the temperature drops. This deviation from simple fluid behavior is particularly strong when water is cooled below the freezing point to the metastable supercooled regime", says Professor Anders Nilsson, Fysikum. Lars G.M. Pettersson, Professor of Theoretical Chemical Physics at Fysikum was awarded a 2021 Advanced Grant from the ERC for the project "Gases in Water". - There is now growing evidence that there are two forms of liquid water: a high density liquid (HDL) and a low density liquid (LDL). The researchers will develop an improved theoretical description of how water molecules interact through computer simulations of the fluids," says Professor Lars G.M. Pettersson.   Further information World Water Day | United Nations World Water Week, August 24-25, 2024 Watch the movie "Water - the strangest liquid" - Fysikum's YouTube channel.

“In the past, we developed many new and powerful techniques with x-ray radiation. The time is ripe now to use them for something important”, says Martin Beye. Climate change is the most important topic to be addressed in the world for the coming decades. Martin commits to make his contribution working at Stockholm University, after his start at Fysikum in September 2023. “At Stockholm University, there is a unique environment, knowledge and infrastructure and wonderful colleagues – all that is required to actually make an impact."

This prize recognizes notable contributions to the field of molecular spectroscopy and dynamics. The prize consists of $10,000, an allowance for travel expenses, up to $1000, to attend the meeting at which the prize is to be presented and a certificate citing the contributions made by the recipient. The motivation is “for seminal contributions in the application of x-ray spectroscopy methods to the molecular dynamics of water and catalytic reactions.”

The conversion of carbon dioxide back into fuels via electrochemistry is a very attractive alternative. - In my studies, I am developing the essential understanding of these reactions by following time-resolved transformation at the atomic and molecular level, says Sergey Koroidov.

When he was in secondary school, he was mostly interested in chemistry and physics. He continued with this focus during the 4-year technical program and during studies abroad. Since then, Professor Anders Nilsson has worked in several countries and his list of publications and awards is long.

Using ultrafast electron diffraction, Anders Nilsson at Stockholm University have participated in a study lead by colleagues at SLAC National Accelerator Laboratory in California on how the structure of water changes after a fast change in the quantum distribution of distances in the internal bond. Upon increasing the quantum number by one unit of the internal OH stretch the team surprisingly found that the hydrogen bond becomes strengthen. The finding is published this week in Nature. Water has a number of unique properties such as ice floats but a solid should be heavier than a liquid, existence of a density maximum, unusual high heat capacity and many more which forms the basis for marine and mammal life on planet Earth. Currently, there exists no quantitative theoretical models based on simulations that can describe these anomalous properties. It was found by Stockholm researchers a few years ago that the anomalous properties of supercooled water are significantly enhance for light water in comparison to heavy water (Science 358, 1589 (2017)). All bonding properties should be identical between the two isotopes except the quantum distribution of the bond length in the waters vibrational motion. This observation points to the importance of nuclear quantum effects also for the anomalous properties. The question is if the quantum effect could be the missing link in theoretical modelling of water to quantitatively describe the anomalous properties?   Atomic Motion in Liquid Water Molecules Often, we think of the H2O molecule in a ball-stick model of fixed distances between the atoms. Even at low temperature there is a zero-point motion of the atoms and in a quantum description the internal OH bond length has a distribution of distances. The experiment performed by the team was to excite the molecules in water using an IR laser with a pulse duration of ≈100 femtoseconds and then use scattering of high energy electrons also with a similar pulse duration. Since a large momentum space of the electron scattering were measured it became possible to convert the data to real space using a simple Fourier Transform technique and detect the correlations of O-O and O-H distances. The experiment was conducted such as there was a variable time delay between the IR laser and the electron beam allowing to follow time dependent distance changes in water upon the IR excitation. At t=0 the OH stretch is excited from v=0 to v=1 generating a different quantum distribution of O-H distances. Within 80 femtoseconds a transient hydrogen bond contraction of roughly 0.04 Å was detected, followed by a thermalization on a timescale of ~1 picosecond. A contraction implies that the hydrogen bond has strengthen. At first, this observation is quite surprising since adding more energy into the OH stretch vibration may easily been assumed to lead to a bond weakening. The results demonstrate the importance of the quantum nature of the vibrational motion of the water molecules for the hydrogen bond and thereby also for the water properties, in-line with the above previous observations. This work involved Anders Nilsson at Chemical Physics, Fysikum, Stockholm University. The study was done in cooperation with SLAC National Accelerator Laboratory, Stanford University, University of California, Davis and University of Nebraska-Lincoln all in the US. Scientist Contact: Anders Nilsson, andersn@fysik.su.se , +46-73 9946230.   More information Further reading in Nature: Direct Observation of Ultrafast Hydrogen Bond Strengthening in Liquid Water by Jie Yang et al: Nature 25 August 2021 (10.1038/s41586-021-03793-9). The first direct observation of atomic motion in liquid water molecules that have been excited with laser light. The results reveal the microscopic origin of water’s strangeness related to the quantum nature of the vibrational motion. (Greg Stewart/SLAC National Accelerator Laboratory)

Recent experiments continue to find evidence for a liquid-liquid phase transition (LLPT) in supercooled water, which would unify our understanding of the anomalous properties of liquid water and amorphous ice. These experiments are challenging because the proposed LLPT occurs under extreme metastable conditions where the liquid freezes to a crystal on a very short time scale.