Heat of adsorption of CO on Pt(1Â 1Â 1) obtained by sum frequency generation vibrational spectroscopy-a new technique to measure adsorption isotherms

CO adsorption on Pt(1 1 1) was studied at temperatures between 373 K and 463 K in a pressure range of 1 × 10−8-3 × 10−5 Torr. Adsorption isotherms were obtained using sum frequency generation, (SFG). By correlating the normalized SFG signal to the surface coverage, the obtained isotherms are in satisfactory agreement with Langmuir adsorption, which is suitable for coverages up to a monolayer. Close to saturation coverage the heat of adsorption was determined to 113(±15) kJ/mol, which is in close agreement to values obtained by single crystal adsorption calorimetry, low energy electron diffraction (LEED) and temperature programmed desorption (TPD) [Y.Y. Yeo, L. Vattuone, D.A. King, J. Chem. Phys. 106 (1997) 392; G. Ertl, M. Neumann, K.M. Streit, Surf. Sci. 64 (1977) 393].