[NewCandle] Measuring Half-Cell Charge

[Frederick Sparber]

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http://www.physics.rutgers.edu/~wchen/Madey_page/Full_Publications/PDF/madey_SSR_1987_T.pdf

2.2.3. Molecular water. bondmg to surfaces
There are several general features which describe the interaction of water
with most surfaces. These generalizations, based both upon experimental and
theoretical studies, are listed below. In these remarks, we do not consider
surfaces at which H,O dissociates, nor hydroxylated surfaces such as silica.
These remarks do apply to most well-characterized surfaces of metals,
semiconductors,
and ionic compounds at which H,O does not dissociate. (Dissociation
of H,O is considered separately in section 3.)
(1) Water bonds through the oxygen atom to the surface. Hydrogen bonds with
the surface (O-H . + . S bonds, where S = surface) are rare. Similarly, water
forms bonds to metal atoms in complexes and clusters via the oxygen atom
[54,55].
(2) Bonding is accompamed by net charge transfer to the surface. Therefore
water acts as a Lewrs base. Charge transfer to the surface manifests itself in a
negative work function change upon adsorption.

Charge donation from adsorbed water to the surface causes the work
function to decrease upon adsorption of H,O. The dipole moment of the
adsorbed molecule can, m principle, be obtained from the experimental value
of the work function change in the lirmt of zero coverage, which IS termed the
"imtral dipole moment". Thts value 1s always only 20% to 50% of the dipole
moment of the isolated H,O molecule (1.83 X lo-'s esu cm), based upon data
presented m sectton 3.2 and table 5 (p. 250). Thts presumably reflects charge