Chemistry Reference
In-Depth Information
Fig. 9.2 Hydration structure
of proton in solvent. (a)
Zundel (H
5
O
2
+
) and (b) Eigen
cation (H
9
O
4
+
)
vanishes for crystalline water ice under normal conditions, it was observed in
water bilayer on Ru(001) [
11
].
In surface chemistry, water-hydroxyl complexes have been particular key spe-
cies in the process of wetting, corrosion, and electrode reaction. Both of experi-
ments and theoretical calculations predicted the first contact layer of water is not
consisted of pure water phase but of a mixture of water and hydroxyl in several
cases [
12
-
21
]. Water-hydroxyl overlayers have been observed on close-packed
metal surfaces in the past. It was unveiled that the existence of hydroxyls leads to
stabilization of water adsorption. The structure of such mixed-overlayers is deter-
mined by the competition between the molecule-substrate and water-hydroxyl
interactions as well as intact water layers. The distance between the adjacent
molecules is strongly affected by the substrate geometry. For instance, the average
distance between the molecules is estimated to be *2.83 Å on Pt(111) and *2.50
Å on Ni(111). In the latter case the d
O-O
is already in the region of a low-barrier H
bond. Recently, PIMD was performed for the water-hydroxyl wetting layer on the
Pt(111), Ru(0001) and Ni(111) surfaces [
22
]. It is revealed that the partial and
entirely symmetric delocalization of the shared H occurs on Pt (Ru) and Ni surfaces,
respectively, highlighting the effect of metal substrates serving to reduce the
classical H transfer barriers within the overlayers. However the water-hydroxyl
interaction, especially its local H-bonding nature, is still unknown at the molecule
level.
9.2 Results and Discussions
9.2.1 Production of Water-Hydroxyl Complexes on Cu(110)
The hydration between a hydroxyl group and a water molecule can be induced by
the STM manipulation. An isolated hydroxyl group is produced by the dissociation
of a water molecule. Figures
9.4
a and b show the sequential images of the reaction
(Fig.
9.4
c is a schematic illustration of the reaction). The black dashed line in the
image represents the atomic row of Cu(110). The hydroxyl group and water
monomer are adsorbed on a twofold short-bridge and on-top site, respectively.
A water and hydroxyl locating on the same atomic row are reacted in Fig.
9.4
a-b
