Periodic Reporting for period 3 - DoMInIon (Dynamics of Molecular Interactions with Ions)
Reporting period: 2024-01-01 to 2025-06-30
Understanding the dynamics of molecular collisions and chemical reactions has been a central research goal in physics and chemistry for more than half a century. In recent years the question of the role of quantum dynamics in chemical reactions has become more and more important. Experiments to investigate such dynamics are, however, challenging and rare. Also theoretical descriptions and numerical simulations still rely mostly on methods from classical mechanics. Given the importance of chemical reactions in all parts of our natural environment, in industrial processes or in biomedical applications, a better understanding of elementary molecular collisions and chemical processes, while intrinsically fundamental research, is of great general interest. In the past years we have spearheaded research on molecular scattering of ions with neutral molecules. Our experiments could provide detailed insight into the dynamics of a range of chemical reactions and allowed us to discover new reaction mechanisms. In this project the objectives are to develop a novel experimental setup to achieve a multifold improved resolution of the product velocities emerging from chemical dynamics studied under single-collision conditions. With this approach we aim to answer the following questions: What are the quantum states of molecules created in such reactions? How do quantum scattering resonances influence the reaction processes? How do reactions proceed in which three products emerge together? How are reactions of charged particles contributing to the radiation damage of in biological cells?
The initial work in the project concentrated on the design and test of the crossed-beam spectrometer. Using our expertise on crossed-beam velocity map imaging, we developed and optimized the design of the new spectrometer to achieve the targeted collision energy resolution. After the arrival of all the parts, the setup was assembled and carefully tested. In this way we could successfully demonstrated the excellent performance of the main components and perform a first crossed-beam reactive scattering measurement. In order to be able to detect two reaction products together, a vacuum ultraviolet laser source was set up that will soon be added to the spectrometer. In parallel to the construction, we carried out reactive scattering measurements using our well-established reaction spectrometer, for comparison with data to be taken with the new spectrometer. In this process we discovered a range of reaction mechanisms in reactions of oxygen radical anions. We also discovered an unexpected and very interesting dynamic isotope effect in a chemical reaction that can only be understood when describing the reaction using a quantum dynamical description.
The unexpected discovery of a dynamic isotope effect, which can only be described by quantum dynamics, represents a substantial progress for fundamental research on chemical dynamics. This result is notable, because it shows the limits of classical theories to describe chemical reactions and thereby shows the dire need to further develop full quantum calculations of chemical processes. With the new crossed beam spectrometer becoming operational, we expect more unexpected results, in particular with respect to quantum-state dependent reactivity of reactions involving three or four atoms, regarding elementary reactions that are important in astrophysics, and on break-up processes of small biological molecules.