Thema der Dissertation:
Quantum effects in collisions between atomis and molecules
Quantum effects in collisions between atomis and molecules
Abstract: Due to their ubiquitous presence throughout the universe, one may scarcely even dare to count the sheer number of collisions between atoms and molecules occurring at any given moment in time. Even so, the laws of nature governing the interaction between such vanishingly small particles have eluded observers for all but a tiny fraction of the history of science. The work presented in this thesis is motivated by the quest to gain an enhanced understanding of collisions governed by quantum mechanics, which might ultimately lead to useful applications such as the control of chemical reactions. To this end, we have leveraged the power of a general and flexible theoretical description of scattering, which, specialised to the case of atoms colliding with diatomic molecules, can be translated into a feasible numerical simulation which is compared and contrasted with ground-breaking experiments, opening avenues for in-depth analysis of quantum effects. At the forefront of these effects are Feshbach resonances, a phenomenon leading to the short-lived formation of ‘quasi-bound’ states between colliding particles due to the resonant coupling between scattering and bound states. Simulations of cold collisions between either helium or neon and dihydrogen or hydrogen-deuterium molecules have been carried out, allowing us, for instance, to gain insight into the role of the nuclear spins of diatomic molecules and its connections to the symmetry of the collision complex. Interestingly, we can show that despite being highly anisotropic, the systems studied here still demonstrate a noteworthy sensitivity to various factors influencing the outcome of the collision. Further, we have turned our attention towards the electronic structure of interacting atoms and molecules, designing, implementing and applying an algorithm to improve ab-initio potential energy surfaces used for cold collisions between helium and dihydrogen molecules by incorporating measured data derived from Feshbach resonance experiments. Obtaining a potential energy surface in this way is in the spirit of machine learning - a widespread and useful tool in the context of electronic structure calculations. Along the way, we have discovered the viability and limitations of adopting different approaches to modifying potential energy surfaces and gleaned a better understanding of their connection to Feshbach resonances. Finally, we have repurposed the simulated data in order to reveal some of the dynamical details of the collision process. Specifically, by regarding the wavepacket of the system as a superposition of the scattering states at many different collision energies, we are not only able to reconstruct the wavepacket at different times during the interaction but also see how some interesting observables change as a function of time. This approach is of interest, for example, in evaluating the trajectory of the interacting particles or to judge whether certain states the system may end up in are populated directly or through intermediate states.
Time & Location
Mar 07, 2025 | 02:00 PM
Hörsaal A (1.3.14)
Fachbereich Physik, Arnimallee 14, 14195 Berlin