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In-Depth Information
Figure 35.
Structure of an
“in-lattice” hydroxide defect in ice.
The oriented graph formalism can be extended to describe defects or impurities
by defining new types of bonds that link water molecules to defects. One may
picture the new bonds as having a different color. This extension was applied to
treat a hydroxyl radical defect in a cubic water cluster [203]. It is also possible to
use the same techniques to describe the interactions of an “in-lattice” hydroxide ion
in an ice Ih lattice [204]. The in-lattice hydroxide corresponds to a graphical vertex
with three incoming and one outgoing directed bond (Fig. 35). To make a periodic
system, it must be compensated by another vertex, like an L-defect. (Notably,
Buch and co-workers [205, 206] show that an “out-of-lattice” configuration in
which the hydroxide hydrogen points into an interstitial space is more stable than
an in-lattice hydroxide. Hence, the out-of-lattice configuration represents a trap for
the hydroxide, and in-lattice a possible intermediate for diffusive motion.) Using
graph invariants to search for low-energy configurations, the lowest energy H-bond
configuration surrounding an “in-lattice” hydroxide ion is found to be the ice XI
structure [204].
VII. CONCLUSION
Our objectives in this work have been twofold. First, to provide a review of
H-bond order-disorder phenomena in water ice and in water clusters. Second,
we have summarized how these phenomena can be described usefully and com-
pactly by exploiting a link between H-bond topology and physical properties. In
