Surface infrared and surface enhanced Raman vibrational spectra of monolayer assemblies in contact with rough metal surfaces

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Abstract
Surface infrared and surface enhanced Raman spectroscopy have been used to obtain the vibrational spectra of monolayer assemblies of cadmium arachidate in contact with a variety of rough silver surfaces. The assemblies were laid down by the Langmuir–Blodgett monolayer deposition technique. The Raman spectra of these assemblies in contact with silver islands show evidence of conformational disorder, i.e., the alkyl chains are not in the all trans configuration. In contrast, the infrared spectra do not show evidence of similar disorder. These results and others, described in the text, are explained by assuming that the infrared photons sense the majority undistorted molecular species, while the Raman photons come from a distorted minority species located in regions where optical electromagnetic fields are enhanced by shape effects, plasmon resonances, etc., of the rough silver surface.