Attenuated-total-reflection study of pyridine overlayers on silver films

We have measured optical properties of pyridine overlayers adsorbed on silver films evaporated in ultrahigh vacuum. These properties are determined from the changes in the surface-plasmon--polariton (SPP) resonance of the silver film that occurs upon adsorption of pyridine. The SPP resonance is detected by the attenuated-total-reflection (ATR) method using the Kretschmann configuration. Submonolayer quantities of pyridine overlayer shift the position of the ATR dip linearly with coverage. The magnitude of the shift is analyzed in terms of several models. With the assumption of saturation coverage of 5×{}10¹⁴ cm^-2, we calculate the effective polarizability of chemisorbed pyridine to be {~}14.5 A³. We also find that the pyridine overlayer undergoes a structural transformation after completion of the first monolayer. The resulting overlayer has a rough surface, and subsequent condensation does not occur in a layer-by-layer fashion.