Generation of harmful slow electrons in water is a race between intermolecular energy decay and proton transfer

When high-energy radiation interacts with water in living organisms, it generates slow-moving particles and electrons that can then damage critical molecules like DNA. Professor Petr Slavíček and his undergraduate student Jakub Dubský from UCT Prague (University of Chemistry and Technology Prague) have described in detail one of the key mechanisms for the creation of these slow electrons in water, a process known as intermolecular coulombic decay (ICD). Their powerful mathematical model successfully explains all the data from complex laser experiments carried out at ETH Zurich (Hans-Jakob Woerner team).

The work, which deepens the fundamental understanding of radiation chemistry, was published in the journal Natural communications.

Detailed knowledge of processes in aqueous solutions, combined with advances in research technologies using high-energy radiation, is transforming the field of radiation chemistry. In the future, this knowledge could lead to significant changes in various fields, including medicine, particularly in the development of more sensitive and controllable applications for devices based on ionizing radiation.

Intermolecular coulombic decay (ICD) was first proven experimentally in water about 15 years ago, but until recently all experiments were carried out on isolated molecules or very small clusters of water. The new research from the Prague-Zurich collaboration is the first to quantify the competition of ICD with proton transfer and nonadiabatic relaxation in liquid water and to establish the isotope dependence.

The study shows that after an internal valence electron is ejected from a water molecule by radiation, the ICD process is not 100% efficient. It is a race against other phenomena, mainly the ultrafast transfer of protons between neighboring water molecules and nonadiabatic relaxation. By performing experiments on ordinary water (H₂O) and heavy water (D₂O), the researchers showed that ICD is more effective in heavy water. This isotope effect confirms that the slower movement of deuterium nuclei gives more time to the electronic decay process, providing clear evidence of competition.

“Our model predicts all the data that the instruments of these difficult experiments can measure,” explains Professor Slavíček. “Therefore, we can also trust it in areas where instruments cannot yet see, and we can explain what happens in a solution after exposure to high-energy radiation.”

The stochastic model is based on data from quantum mechanics, which can usually only be calculated for limited systems such as single water molecules or small clusters. These inputs, combined with experimental results, were developed into a probabilistic model that provides a comprehensive picture of DCI in a realistic environment.

It is notable that the author of the published stochastic model is Jakub Dubský, who recently completed his bachelor’s degree at UCT Prague and is preparing to continue his master’s studies at the University of Oxford.

“It’s extraordinary when an undergraduate student carries out work at the level of a doctoral student, resulting in a real, working product that provides completely new knowledge,” adds Professor Slavíček, praising his student’s contribution.