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sure (i.e., increasing the rate of the reaction) cannot alleviate this problem. The attainment of a limiting conversion due to isolation of active sites has been observed in many other solid-state polymerizations.23,24The dependence of conversion on polymerization pressure and annealing of the films prior to irradiation highlights the influence of morphology on gas-water interface polymerizations. The structural changes that occur in a monolayer of vinyl stearate upon polymerization can be understood by postulating the existence of crystallite "islands". This same model has been used to explain the morphology of a variety of monolayer films. 14'17,25'28 The distance between islands decreases with increasing surface pressure. The packing of the islands is pressure and time dependent. High surface pressures and long annealing times increase the effective crystallite size since these conditions permit neighboring islands to pack close to one another. Annealing removes defects which could be present in the film by providing enough time for the islands to pack closer and more efficiently.Electron microscopy studies by Ries and Walker have indicated the presence of crystallite islands in monomolecular films.26'28 An increase in surface pressure was shown to decrease the distance between adjacent islands.High surface pressures increased the effective crystallite size by causing neighboring islands to merge into one large island.

This report details a series of experiments and calculations designed to provide a more complete analysis of the factors which play contribute to the quenching of the SERS response at Pb-modified Ag electrodes. SERS intensity-Pb coverage profiles are presented for the pyridine ring-breathing vibration after the majority of atomic-scale roughness features are destroyed by Pb monolayer deposition. Comparison of the morphology of the intensity-coverage profiles obtained during and after the loss of atomic-scale roughness indicates that loas of the majority of atomic-scale roughness during Pb deposition cannot fully account for the observed quenching of the SERS response. The SERS response of 3,6-dihydroxypyridazine (DHPZN) is examined in order to evaluate the impact of adsorbate coverage on the observed quenching behavior. X-ray photoelectron spectroscopic studies of DHPZN adsorbed at Ag and Pb-modified Ag electrodes indicate that changes in the adsorbate surface coverage during Pb deposition do not contribute significantly to the quenching of the SERS response. Theoretical SERS enhancement-Pb coverage profiles based on two different electromagnetic predictions and previously calculated optical constants for Pbmodified Ag surfaces are presented. The functional form of the linear approximation expression used for evaluation of surface optical constants from differential reflectivity data is examined in order to provide further insight into the role of surface electronic properties in the SERS mechanism(s).