Kinetic parameters of CO adsorbed on Pt(111) studied by in situ high resolution x-ray photoelectron spectroscopy

The kinetics of the adsorption system CO/Pt(111) has been studied by time-resolved high-resolution x-ray photoelectron spectroscopy using third generation synchrotron radiation at BESSY II. CO is dosed by a supersonic molecular beam device which allows for a high sample pressure (here up to ${10}^{\text{−6}}\hspace{0.17em}\mathrm{mbar})$ and a fast switching of the pressure. The site-specific occupation of CO adsorbed on on-top and bridge sites is determined quantitatively from $\mathrm{C}\text{\hspace{0.05em}1s}$ spectra, which can be taken with a minimum collection time of 1.5 s per spectrum. Based on the observation of thermal equilibrium between the two sites, we perform a phenomenological analysis of the data, assuming a constant binding energy difference $\mathrm{\Delta E.}$ From the on-top/bridge occupation ratio as a function of coverage obtained by uptake measurements we extract a value of $\text{ΔE=41\hspace{0.17em}}\mathrm{meV}.$ With the same ansatz, $\mathrm{\Delta E}$ is calculated from temperature-dependent measurements at a constant coverage. Finally, determination of the coverage during isothermal desorption is used to obtain the total binding energy of CO on Pt(111). Differences between our evaluation methods and literature reports are discussed.