Relative Raman scattering cross sections for chemisorbed and physisorbed pyridine molecules adsorbed on surface-enhanced Raman-scattering-active Ag films in ultrahigh vacuum: Local-field effects in the low-coverage regime.

摘要: We have studied the Raman scattering from pyridine adsorbed on silver films evaporated cleaved mica (100 K) in ultrahigh vacuum. These only a small number of chemisorption sites (approx.2%). The are filled preferentially during initial stages adsorption, followed by filling physisorption sites. Both physisorbed and chemisorbed exhibit strongly enhanced scattering. At one monolayer coverage average enhancement is factor-of-55 larger for molecules. When pyridine-d/sub 5/ molecules used to saturate sites, subsequent adsorption pyridine-h/sub results partial displacement This phenomenon allows us measure ratio cross sections neighborhood less than 4. Combining this measurement with factor-of-55-larger overall compared phys- isorbed molecules, we conclude that (including those just physisorbed) site an extra enhancement. also analyzed dependence intensity found it be well described simple depolarization model. optical polarizability thismore » model approx.10 A/sup 3/. value essentially same as reported annealed surface-enhanced Raman-scattering-inactive films.« less