Berlin 2018 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 68: Surface dynamics: Reactions, elementary processes and phase transitions I
O 68.2: Vortrag
Mittwoch, 14. März 2018, 15:15–15:30, MA 043
Analyzing and Tuning the Energetic Landscape of H2Pc Tautomerization — •Lucas Klein1, Jens Kügel1, Markus Leisegang1, and Matthias Bode1,2 — 1Physikalisches Institut, Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany — 2Wilhelm Conrad Röntgen Center of Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, 97074 Würzburg
Many chemical and biological reactions are associated with the quantum tunneling
of hydrogen atoms through a potential barrier in the reaction path [1].
Whereas quantum tunneling is often identified by temperature-dependent measurements
or a large kinetic isotope effect, we demonstrate a new method working at a fixed temperature.
As a model system we used the tautomerization—the switching of hydrogen protons
between different adsorption sites—of phthalocyanine (H2Pc) molecules
adsorbed on a Ag(111) surface which are probed by scanning tunneling microscopy.
We will show, that the tautomerization of this molecule
is exclusively triggered by the excitation of the N–H stretching mode.
Interestingly, a step-like increase of the tautomerization rate is observed
at a bias voltage that corresponds to the second harmonic of this vibrational mode,
which we attribute to a crossover from quantum tunneling
through the tautomerization barrier to an excitation over the barrier.
This explanation is further supported by modifying the energetic landscape
of the tautomerization of pristine H2Pc by single silver atom manipulation and/or deprotonation.
[1] M. Koch et. al., J. Am. Chem. Soc. 139, 12681-12687 (2017)