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Raman Spectra of Adsorbed Heterocyclic Molecules on Silica

Raman spectroscopy has been employed in several investigations of oxide surfaces. The technique appears to have a number of advantages over infrared absorption spectroscopy, which has been one of the more informative techniques in the study of surfaces and surface-absorbed molecules. The low Raman intensity of the spectrum of the silica substrate through the fingerprint region (700 to 2000 cm−1) permits the detection of structure-sensitive vibrations of the adsorbate molecule. This often allows the nature and degree of perturbation of the adsorbate molecule on the surface to be deduced. In addition, the technique is a sensitive method of studying the vibrations of symmetrical molecules on a surface. Further, Raman spectroscopy may provide a convenient means of detecting low energy transitions associated with H-bond formation and with torsional vibrations of the adsorbate. The principal limitation on the technique, at present, appears to be the restriction set on the amplification of the spectrum by the intensity of the background Raman scattering and the background emission continuum (i.e., so-called