Attosecond measurement on electrons in water clusters
A view of the attosecond laboratory: The vacuum chamber, inside of which water clusters are ionised by laser pulses, is seen on the left. Credit: ETH Zürich / H.J. Wörner

The majority of important chemical processes take place in a single solution. In such processes, a decisive role is played by electrons that are exchanged between different atoms. The details of how that happens are hard to understand.

The dynamics of electrons in clusters made of water molecule with a time resolution of just a few attoseconds have been studied by a group of researchers. Their results were published in a journal.

There is a time delay in ionized gasses.

Scientists studied how water is ionized by a short laser pulse. Water is squeezed through a tiny nozzle under high pressure to create clusters. One electron of the cluster pulse can be released from the laser's energy. The "hole" is a result of this.

After a brief delay, the release of the electron occurs. The delay is dependent on the distribution of the electron hole. Xiaochun Gong, the post-doc who was in charge of the project, said that the distribution of the hole could only be calculated theoretically.

The resolution is attosecond.

A few billionths of a second is how long the delay is. The number of attoseconds in a singlesecond is roughly the number of seconds in 32 billion years.

To measure the extremely short periods of a few attoseconds, Wrner and his colleagues split up a very intense laser pulse into two parts, one of which was converted to the extreme ultraviolet. They focused on the water clusters.

The electrons were ejected by the ultraviolet laser. An interferometer could be used to tune the phase of the laser. Depending on the phase, the number of ionized events varied. The researchers were able to read off the delay from those measurement.

Wrner's group was able to show that the delay depends on the size of the water cluster. The delay increases as the cluster size increases. It stays the same for five or more water molecule. The high degree of symmetry exhibited by small clusters allow the electron hole to spread out across the whole cluster according to the rules of quantum mechanics. lager clusters are asymmetric and disorganized and thus the hole is on a few water molecule.

Semiconductor applications as well.

New research opportunities have been opened up by the attosecond measurement. He wants to resolve the dynamics of the electron hole both temporally and spatially in follow up experiments. Wrner hopes that this will lead to a better understanding of how radiation damage develops in biological tissue, since water plays a major role in that process.

Research on electron dynamics in water is just one of the possibilities Wrner sees. To realize faster electronic components, a profound understanding of the spatial extension of electron and hole states is necessary. The new technique could be very useful here.

More information: X. Gong et al, Attosecond spectroscopy of size-resolved water clusters, Nature (2022). DOI: 10.1038/s41586-022-05039-8 Journal information: Nature