A model for Raman-active librational modes on a metal surface. Pyridine and CN^- on silver

A physical model is presented for the origin of very low frequency librational modes seen in the enhanced Raman spectrum of pyridine and CN- on an electrochemically prepared silver surface The image dipole of the molecule provides a anharmonic restoring torque for molecules adsorbed with their dipole moment perpendicular to the surface. The calculated librational modes are in reasonable agreement with experiment. © 1980.