Chemistry Reference
In-Depth Information
having the potential minimum, resulting in the lower barrier of the rotation.
Secondly, the strength of the interaction between water and metal surface affect
dynamics, especially on the diffusion process, which is expected as following:
Au \ Ag \ Cu \ Pd \ Pt \ Ru \ Rh. For instance, based on DFT calculations
the adsorption energies are predicted to be 0.24, 0.33, 0.35, and 0.38 eV for
Cu(111), Pd(111), Pt(111), and Ru(0001), respectively [
18
]. It is deduced that the
strong water-surface interaction on Pt(111) or Ru(0001) pins the donor molecule
and suppresses the intrinsic motion of water dimer, while the mediate interaction
on Cu(110) brings it into prominence.
5.3 Summary
The donor-acceptor interchange within a water dimer isolated on a Cu(110)
surface was imaged and characterized using STM. The interchange can be
observed as two states fluctuating image. Using the time-resolved measurement the
voltage and current dependence of the interchange rate were investigated. It was
found that there is no voltage and current dependence below V
s
= 40 mV, indi-
cating the interchange is not induced by STM, thus intrinsic to a water dimer.
Furthermore the large isotope effect (*60) was quantified in the intrinsic inter-
change rate between (H
2
O)
2
and (D
2
O)
2
, suggesting that quantum tunneling is
involved in the process. The excitation of the donor-substrate stretch mode was
found to effectively assist the interchange tunneling, highlighting the sensitivity of
the interchange dynamics to the displacement of oxygen atoms. The structure and
the interchange pathway were determined by DFT calculations. The barrier cal-
culated for the interchange (0.24 eV) cannot be overcome by mere thermal acti-
vation at 6 K, supporting the experimental results that the interchange takes place
via tunneling.
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