Chemistry Reference
In-Depth Information
Chapter 4
Water Monomer: Structure and Diffusion
of a Single Water Molecule
Abstract I describe the structure and diffusion of a single water molecule isolated
on a Cu(110) surface in this chapter. The monomeric adsorption of water mole-
cules can be realized at low temperature (\20 K). The adsorption structure is
determined with the help of DFT calculations. A water molecule chemisorbs on a
top of Cu atoms and thermally diffuses on the surface along the atomic row of
Cu(110) even at 6 K. Using the time-resolved measurement of the STM, the
diffusion rate is determined to be 0.13 s
-1
that corresponds to the barrier of
*15 meV. The diffusion is also induced by the vibrational excitation of water
molecule via the inelastic electron tunneling process. I also show the controlled
manipulation of individual water molecules. A water molecule can be moved
along the atomic row direction by the lateral manipulation of STM.
Keywords Water monomer
Adsorption geometry
Surface diffusion
Molecule
manipulation
4.1 Introduction
The adsorption of an isolated water molecule on metal surfaces provides a
fundamental understanding about a bare interaction between a water molecule and
metal surfaces. The question is simple as follow; where and how a water molecule
adsorbs on a metal surface. In contrast with this simple question, the experimental
characterization of an isolated water molecule is extremely difficult due to a facile
clustering of molecules. In order to minimize the clustering, it is essential to perform
experiments at extremely low coverages of water and at low temperatures.
Monomeric water is not observed on most of noble metal surfaces even at liquid
nitrogen temperature and it becomes possible below 20 K. On the basis of the
molecular orbital of a free water molecule, it is expected that the interaction of water
with a metal surface would be via the non-bonding, or lone pair electrons on the
