Saccharin (o-benzoic sulfimide) preferentially adsorbs onto platinum(1
11)electrodes modified with the (3x3) iodine adlayers (theta(1) = 0.44
). This is in contrast to platinum (111) electrodes modified with the
(root 7x root 7)R19.1 degrees iodine adlayer (theta(1) = 0.43) where n
o adsorption is detected. Saccharin adsorption was monitored through c
hanges in the voltammograms associated with the oxidative desorption o
f the strongly bound iodine adlayer and Ag underpotential deposition o
n the iodine-modified electrode surfaces in acidic solutions. Simple m
odeling calculations support the experimental observation and suggest
that the preferential adsorptive behavior of saccharin is due to the e
nhanced van der Waals interactions associated with the symmetric Pt(11
1)(3x3)-I adlayer structure. The Pt(111)(3x3)-I adlayer structure is o
ne of two (3x3) iodine adlayer structures found to a comparable extent
of coverage on name-annealed Pt(111) electrodes exposed to iodine for
a longer duration than that leading to the formation of the Pt(111)(r
oot 7x root 7)R19.1 degrees-I adlattice.