Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 16: Organic, Polymeric, and Biomolecular Films I
O 16.1: Vortrag
Montag, 26. März 2007, 14:15–14:30, H42
Molecular Chirality uncovered - Circular Dichroism of Adsorbed Chiral Molecules — •Thorsten Kampen1, Philipp Martin Schmidt1, Jeong Won Kim2, Hugo Dil1, and Karsten Horn1 — 11 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany — 2Nano-Surface Group, Korea Research Institute of Standards and Science, Daejon, Korea
The chirality of molecules is an intrinsic structural property that has a huge impact upon biological and chemical reactions. However, the identification of the chiral nature of molecules in the adsorbed phase has been proven difficult. Here, we report on the characterization of adsorbed chiral molecules with respect to handedness and chemical composition using photoemission spectroscopy with circular polarized light. The emission from the carbon atoms in tartaric acid adsorbed on Cu(110) surfaces shows circular dichroism, and the asymmetry changes sign as a function of the emission angle. Changing the handedness of the molecule reverses the sign in the measured asymmetry. No asymmetry in the angular distribution is observed for the achiral meso-tartaric acid. Alanine and cysteine are two amino acids with the same next-neighbor environment of the chiral center, with cysteine containing an additional sulfur atom in the end group. This difference leads to different adsorption behavior and opposite optical activity. However, the circular dichroism in core-level photoemission is identical for both molecules.
The above mentioned results show that the angular dependent asymmetry is an absolute representation of the molecular chirality.