Adsorption and decomposition of hydrocarbons on platinum black: Vibrational modes from NIS

The adsorption and decomposition of acetylene and ethylene on platinum black have been investigated by neutron inelastic scattering (NIS) studies of the vibrations of chemisorbed species in the energy range 30–200 meV. Results are compared in detail with electron energy loss spectroscopy (EELS) data and with spectra of model inorganic complexes. The NIS spectra for C2H2 and C2H4 chemisorbed at 120–150 K exhibit a number of spectral features (from both the internal modes and modes associated with vibrations against the surface metal atoms) which are in general agreement with EELS results for Pt(111). Detailed comparison of the spectral peak intensities and positions with various models for the adsorbed molecules rule out linear (C2H2) or planar (C2H4) species and are consistent with bent molecular configurations on the surface. Bond angles and force constants are derived from the model fits to the neutron data in each case. The NIS spectra of a ‘‘saturated’’C2H2 monolayer warmed to 300 K indicates a rearra...