A theoretical study of vibrational lineshapes for simple molecules adsorbed on surfaces: a classical trajectory approach

The use of classical trajectories in determining vibrational spectra for diatomic molecules adsorbed on surfaces is presented. In partieular, the effects of anharmonic coupling between high frequency intramolecular modes and low frequency frustrated translations (so called T₂ processes) has been investigated. The model has been successful in interpreting the i.r. absorption spectroscopic data for CO/Pt(111) of HAYDEN and BRADSHAW and results for this system will be presented. To simulate effects arising from coupling to the substrate heat-bath (electron-hole pairs and phonons), a phenomenological damping has been included. This allows an estimate to be made of the relative importance of true dissipative processes ( T₁), to the dephasing contribution to the linewidth.