Structural and vibrational properties of the carbonyl sulfide (OCS) covered NaCl(100) surface

The structure and dynamics of a physisorbed OCS monolayer on the in situ cleaved NaCl(100) surface have been studied by elastic as well as inelastic helium atom scattering (HAS) in the temperature range 30-100 K. OCS adsorbs on NaCl(100) via the formation of large islands. The commensurate overlayer consists of domains which are rotated 90 degrees with respect to each other and have (2 x 1) unit meshes. Desorption spectra with simultaneous surface coverage monitoring by HAS were used to roughly estimate the surface-adsorbate binding energy to be about 0.26 eV. Phonon spectra from an OCS monolayer were measured in the [100] direction. At least eight modes with energies below 10 meV were observed. The phonon peak intensities were analyzed as a function of parallel momentum transfer in order to distinguish modes with predominantly transversal or longitudinal polarization.