The chemisorption site of the simplest prototypical model alkanethiol compound, methanethiol [CH3SH], on a Pt{111} surface in the temperature range 298-1073 K has been investigated by means of time-of-flight scattering and recoiling spectrometry (TOF-SARS) and low-energy electron diffraction (LEED). TOF-SARS spectra of the scattered and recoiled ions plus fast neutrals were collected as a function of crystal azimuthal rotation angle delta and beam incident angle alpha using 4 keV Ar+ primary ions. At room temperature, the adsorption of methanethiol produces a partially disordered overlayer that gives rise to a diffuse (root 3x root 3)R30 degrees LEED pattern and three-fold symmetry in the scattering profiles. Heating this surface layer results in the sequential dehydrogenation of the methanethiol and the formation of S-C species at elevated temperatures. By similar to 373 K, hydrogen is absent from the TOF-SARS spectra and a sharp (root 3x root 3)R30 degrees LEED pattern is observed. The model developed from the scattering data is consistent with the preservation of the adsorption site at elevated temperatures, but a change in the S-C bond angle with respect to the surface plane. For the fully dehydrogenated species, the S atoms reside similar 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 Angstrom in hexagonal-close-packed (hcp) three-fold sites. It is proposed that the remarkable stability of this SC adsorbate results from bonding 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. [S0021-9606(98)70245-4].