Adsorption Sites of CO on the (111) Face of Pt10Ni90 Single-Crystal Alloy
The surface vibrations of CO chemisorbed at room temperature on the close-packed (111) face of Pt-Ni single crystal alloy (10 atom % Pt) have been investigated by vibrational electron energy loss spectroscopy. During adsorption two well-separated CO stretching modes develop at respectively 1820 ± 10 and 2070 ± 10 cm−1 while, in the low frequency region, a well defined loss peak at 440 ± 10 cm−1 and a shoulder near 365 cm−1 appear simultaneously. The 2070 cm−1 loss peak, lower than the 1820 cm−1 peak for small exposures (< 0.35 L), dominates the spectrum at saturation in our experimental conditions (exposure ≥ 1.5 L, 300 K, PCO < 10−8 Torr): I2070/(I2070 + I1820) = 64%. These vibrations are attributed to CO molecules adsorbed linearly (2070 and 440 cm−1) and multi-bonded (1820 and ~ 365 cm−1) respectively.