Infrared spectra of high coverage CO adsorption structures on Pt(111)

The adsorption of carbon monoxide on Pt(111) was studied using polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) and sum frequency generation (SFG) spectroscopy. Two CO on-top signals at 2110 cm(-1) and 2097 cm(-1) have been detected under continuous CO exposure in a pressure range from 10(-7) to 100 mbar and at temperatures between 200 K and 300 K. The formation of the higher wavenumber signal is found to be kinetically limited below 200 K and by the presence of a stable c(4 x 2) adlayer in UHV. On the basis of the results presented in this study and previous experimental findings the two on-top signals are related to different CO compression layers on Pt(111) with theta>0.5, hexagonal Moire lattices and rectangular coincident site lattices. (C) 2010 Elsevier B.V. All rights reserved.