Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 139, Issue 36, Pages 12681-12687Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.7b06905
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Funding
- Morino Foundation for Molecular Science
- EPSRC [EP/L000202, EP/K000225/1]
- Polish National Science Centre [DEC-2013/10/M/ST4/00069]
- EPSRC [EP/L000202/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/L000202/1] Funding Source: researchfish
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Quantum tunneling of hydrogen atoms (or protons) plays a crucial role in many chemical and biological reactions. Although tunneling of a single particle has been examined extensively in various one-dimensional potentials, many-particle tunneling in high-dimensional potential energy surfaces remains poorly understood. Here we present a direct observation of a double hydrogen atom transfer (tautomerization) within a single porphycene molecule on a Ag(110) surface using a cryogenic scanning tunneling microscope (STM). The tautomerization rates are temperature independent below similar to 10 K, and a large kinetic isotope effect (KIE) is observed upon substituting the transferred hydrogen atoms by deuterium, indicating that the process is governed by tunneling. The observed KIE for three isotopologues and density functional theory calculations reveal that a stepwise transfer mechanism is dominant in the tautomerization. It is also found that the tautomerization rate is increased by vibrational excitation via an inelastic electron tunneling process. Moreover, the STM tip can be used to manipulate the tunneling dynamics through modification of the potential landscape.
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