Vibrations of potassium at Pt(111) and formation of KOH studied by electron energy-loss spectroscopy

We have characterized the adsorption of K at the Pt(111) surface at room temperature by electron energy-loss spectroscopy. The vibrational frequency of adsorbed K adatoms shifts from 135 cm(-1) at low coverages to 175 cm(-1) at a coverage of theta(K)=0.16. This frequency shift can be explained by lateral dipole-dipole interactions between the adsorbed alkali metal atoms. For K coverages up to theta(K)=0.33 the frequency dl:creases to 155 cm(-1) and the loss intensity nearly vanishes, which is attributed to the metallization of the alkali metal layer. Above K coverages of about theta(K)=0.10, the adsorbed K reacts with residual water molecules to form KOH, with the K atom bonding to platinum. Vibrational modes at 120, 230, 770 and 3658 cm(-1) are characteristic of this compound and are assigned to the Pt-K, the K-O stretching, the OH bending and the O-H stretching vibrations, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.