A novel H(2) molecular adsorption state on metal surfaces has been detected by temperature-programmed desorption and electron energy loss spectroscopy experiments of the H(2)/Pd(210) system. The molecular nature of this state has been verified by isotope exchange experiments. This molecular state leads to a decrease of the surface work function while atomic hydrogen on Pd(210) causes an increase. Ab initio total-energy calculations have confirmed all experimental findings. Through these calculations the microscopic nature of this novel molecular adsorption state could be identified; it turns out that this state is stabilized by the presence of atomic hydrogen on the Pd(210) surface.
The protonation/deprotonation of methyl orange adsorbed on a smooth platinum electrode has been investigated by modulated reflectance spectroscopy in the visible spectral region. The modulated reflectance spectra are mainly governed by the potential modulation of the protonation equilibria of methyl orange and the buffer (acetate/acetic acid), respectively. The pK values of the protonation equilibria within the adsorption layer change with the electrode potential E in the following way: dpK/dE = 0.8 V−1 and —1.0 V−1 for methyl orange and acetic acid, respectively.
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