AVS 64th International Symposium & Exhibition
    Fundamental Discoveries in Heterogeneous Catalysis Focus Topic Thursday Sessions
       Session HC+SA+SS-ThM

Paper HC+SA+SS-ThM5
Imaging the Molecular Origins of Symmetry Breaking on Well-defined Surfaces

Thursday, November 2, 2017, 9:20 am, Room 24

Session: Mechanisms and Reaction Pathways in Heterogeneously Catalyzed Reactions
Presenter: Amanda Larson, Tufts University
Authors: A.M. Larson, Tufts University
R.T. Hannagan, Tufts University
E.C.H. Sykes, Tufts University
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Understanding the interaction of prochiral reactants with chiral modifiers on surfaces is a key step towards controlling heterogeneous enantioselective catalysis. We have chosen a simple model system composed of interacting chiral propylene oxide and propene molecules on a Cu(111) surface that is amenable to both scanning probe and desorption studies. Low temperature scanning tunneling microscopy (STM) enables an unprecedented level of spatial resolution of the enantioselective molecule-molecule interactions and their dynamics. STM imaging of propylene oxide and propene molecules at 5 K reveals that both molecules, when in isolation on the surface, behave as molecular rotors. Furthermore, the chirality of individual propylene oxide molecules can be discerned from the STM images of the rotating molecule. While propene is achiral in the gas phase it become chiral when bound to surfaces and STM also allows us to distinguish between its surface-bound enantiomers. When studied separately, repulsive forces between both sets of molecules disperse them on the surface at low coverages. However, when co-dosed we observe an attraction between propylene oxide and propene and they form complexes in which their rotation is inhibited. Temperature programmed desorption measurements are used to quantify these chiral modifier-molecule interaction strengths. Finally, the geometry of individual propene and propylene oxide molecules can be determined within the complexes and 1:1 chiral interactions deciphered.