Web Release Date: July 26,
Adsorption and Desorption of HCl on Pt(111)
and
Environmental Molecular Sciences Laboratory and Fundamental Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Mail Stop K8-88, Richland, Washington 99352, and Département de Chimie, Université de Sherbrooke, 2500 Boul. Université, Sherbrooke, Québec J1K 2R1, Canada
Received: April 26, 2005
In Final Form: June 14, 2005
Abstract:
The adsorption and desorption of HCl on Pt(111) is investigated by temperature programmed desorption,
infrared reflection absorption spectroscopy, and low energy electron diffraction. Five peaks are identified in
the desorption spectra prior to the onset of multilayer desorption. At low coverage (
< 0.25 monolayers
(ML)), desorption peaks at ~135 and 200 K are observed and assigned to recombinative desorption of
dissociated HCl. At higher coverages, desorption peaks at 70, 77, and 84 K are observed. These peaks are
assigned to the desorption of molecularly adsorbed HCl. The infrared spectra are in agreement with these
assignments and show that HCl deposited at 20 K is amorphous but crystallizes when heated above 60 K.
Kinetic analysis of the desorption spectra reveals a strong repulsive coverage dependence for the desorption
energy of the low coverage features ( < 0.25 ML). The diffraction data indicate that at low temperature the
adsorbed HCl clusters into ordered islands with a (3 × 3) structure and a local coverage of 4/9 with respect
to the Pt(111) substrate.
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