Vibrational Analysis of Single Molecule Chemistry: Ethylene Dehydrogenation on Ni(110)

The dynamics and chemistry of individual ethylene molecules adsorbed on the Ni(110) surface at 13 K have been studied with a variable temperature scanning tunneling microscope (STM). By applying a voltage pulse to a single ethylene molecule, the tunneling electrons cause the molecule to reversibly hop away from and back under the tip. The five ethylene isotopes hop at different rates. A larger voltage pulse (1.1−1.5 V) induces dehydrogenation, and a strong primary isotope effect is observed. By using inelastic electron tunneling spectroscopy (IETS) with the STM, we identified the dehydrogenated products from the characteristic vibrational energies as acetylene. This identification is further supported with STM-IETS on single acetylene molecules adsorbed directly from the gas phase. Two different types of acetylene exist on the surface. They can be distinguished in the regular STM image, and they exhibit shifted vibrational peaks. Applying another voltage pulse (1.0 −4.8 V) further dehydrogenates acetylene to carbon atoms.