Dynamics of Adsorption and Desorption on Chiral Surfaces

The relationship between structural chirality and chiral motion is not well understood and often involves different length scales for both phenomena. In this thesis, a dispersion-corrected density functional theory study focusses on the dissociative adsorption reaction of small molecules on both chiral and achiral surfaces. The interplay between chirality and surface dynamics is explored by using the transition state of the dissociation reaction as a starting point for ab-initio molecular dynamics simulations of the subsequent desorption. Special focus in the analysis of these reactive trajectories lies on the time evolution of rotational momenta. To that end, molecules with different degrees of rotational symmetry were chosen as model systems. Methane (spherical top), ethane (prolate symmetric top) and formic acid (asymmetric top) were studied with respect to their rotational behaviour upon desorption from either platinum or copper surfaces. With decreasing molecular symmetry, these molecules show an increasingly visible difference between the influence of the chiral surface and the achiral surface on the rotational properties of the desorbing molecules. Particularly for formic acid on the chiral Cu{531} surface, a much larger and more directed effect on the molecular rotation was observed, with only one rotational sense, a significant and non-vanishing surface-normal component, and a much narrower spread of the angular momentum vector compared to the achiral surface. In addition, the study of both enantiomers of alanine (a chiral asymmetric top) desorbing from R-Cu{531} revealed a pronounced diastereomerism. S-alanine molecules exhibit a larger angular momentum, with a clear preference for one rotational sense, whereas no such preference is observed for R-alanine molecules upon desorption from this surface, thus seemingly cancelling out any chiral influence of the surface. These effects have the potential to open up entirely new applications for chiral surfaces, e.g., in chiral recognition or chiral resolution processes, and inspire the design of new experiments. Finally, it was explored to what extent the intermediate axis phenomenon applies to molecules as non-rigid, vibrating bodies. Some evidence was gathered that the equations which define the time-dependence of this phenomenon for rigid bodies also describe the behaviour of molecules to a good approximation. There are, however, some systematic deviations that are unique to molecules and their vibrations and cannot be derived from a rigid-body approach.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Matysik, Sabine

Advisor dc:contributor.advisor

• Jenkins, Stephen

• Chirality
• Surface Science
• Computational Chemistry
• DFT

Licence

• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0002-7305-5171

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/341229