CHEMISORPTION SITE OF METHANETHIOL ON PT(111)

The chemisorption site of the simplest prototypical model alkanethiol compound, methanethiol [CH3SH], on a Pt{111} surface in the temperatur e range 298-1073 K has been investigated by means of time-of-flight sc attering and recoiling spectrometry (TOF-SARS) and low-energy electron diffraction (LEED). TOF-SARS spectra of the scattered and recoiled io ns plus fast neutrals were collected as a function of crystal azimutha l rotation angle delta and beam incident angle alpha using 4 keV Ar+ p rimary ions. At room temperature, the adsorption of methanethiol produ ces a partially disordered overlayer that gives rise to a diffuse (roo t 3x root 3)R30 degrees LEED pattern and three-fold symmetry in the sc attering profiles. Heating this surface layer results in the sequentia l dehydrogenation of the methanethiol and the formation of S-C species at elevated temperatures. By similar to 373 K, hydrogen is absent fro m the TOF-SARS spectra and a sharp (root 3x root 3)R30 degrees LEED pa ttern is observed. The model developed from the scattering data is con sistent with the preservation of the adsorption site at elevated tempe ratures, but a change in the S-C bond angle with respect to the surfac e plane. For the fully dehydrogenated species, the S atoms reside simi lar to 1.6 +/- 0.2 Angstrom above the surface in face-centered-cubic ( fcc) three-fold sites and the C atoms reside similar to 1.5 +/- 0.4 An gstrom in hexagonal-close-packed (hcp) three-fold sites. It is propose d that the remarkable stability of this SC adsorbate results from bond ing of both the S and C atoms to the surrounding Pt atoms, i.e., a Pt- stabilized SC moiety. (C) 1998 American Institute of Physics. [S0021-9 606(98)70245-4].