Abstract
The adsorption of CO on Pt(111) was studied by picosecond infrared-visible
sum frequency generation (SFG) vibrational spectroscopy in a pressure
range from 10-7 to 500 mbar and in a temperature range of 160-400
K. At low pressure the experiments were complemented by TPD, LEED,
and AES. Terminally bonded (on-top) CO was the only species observed
between 160 and 400 K, independent of gas pressure. The CO stretching
frequency was blue-shifted by about 15 cm-1 with increasing pressure
(up to 2097 cm-1), but no evidence for high-pressure CO species or
surface roughening was found. The influence of defects was also investigated.
CO adsorption on a defective (nonannealed) Pt(111) surface yielded
peaks that were slightly broadened but otherwise identical to the
defect-free surface. At 160 K, a second peak at 2085 cm-1 evolved
above 50 mbar of CO. TPD revealed that under these conditions residual
(contaminant) water adsorbs on the surface. The coadsorption of water
and CO red-shifted the terminal CO peak by about 15 cm-1, resulting
from the substrate-mediated interaction of CO and water.
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