Article,
On the adsorption of CO on Pt(111)
Surf. Sci., 123 (2-3): 264 - 282 (1982)
DOI: DOI: 10.1016/0039-6028(82)90328-4
Abstract
The adsorption system Pt(111)-CO has been investigated with LEED,
thermal desorption and vibrat on spectroscopy using electron energy
losses (EELS). Upon adsorption around 100 K at low coverages (theta
less, approximate 0.33) spontaneously ordered overlayers of CO,
not observed before, have been found. At higher coverages the superstructures
exhibit a substantial disorder at low temperatures, but transform
into well ordered structures with defined diffraction patterns if
the sample is annealed and subsequently cooled down again. The structures
have been characterized according to the binding types of CO by their
vibrational spectra. Up to a coverage of about 0.17 CO is exclusively
linearly bonded in on-top sites. At coverages above 0.17 bridge sites
are occupied in addition. At 100 K the adsorbate exhibits an island
structure. The growth of islands is reflected in the coverage dependence
of the sticking probability which passes through a maximum. At 300
K the sticking probability is further influenced by a precursor state
making the sticking probability almost coverage independent within
a certain range. In the vibration spectra multiple losses, combination
bands and overtones have also been observed. From the overtones of
the #dipole##forbidden# hindered rotations of the molecule the fundamental
frequencies of the CO bending modes can be estimated to 410 and 360
cm-1 for linear- and bridge-bonded CO, respectively.
