4-Pyridine-carboxylic acid, Raman

The vibrational spectrum of 4-pyridine-carboxylic acid on alumina in Fig. 4d is equivalent to an infrared or Raman spectrum and can provide a great deal of information about the structure and bonding characteristics of the molecular layer on the oxide surface. For example, the absence of the characteristic > q mode at 1680 cm 1 and the presence of the symmetric and anti-symmetric O-C-O stretching frequencies at 1380 and 1550 cm indicate that 4-pyridine-carboxylic acid loses a proton and bonds to the aluminum oxide as a carboxylate ion. 

SERS was discovered with pyridine. Other aromatic nitrogen- or oxygen-containing compounds, such as aromatic amines or phenols, also display strong enhancement due to SERS. The enhancement can also be seen with other electron-rich analytes such as carboxylic acids. Although SERS allows easy observation of Raman spectra from solutions with concentration in the micromolar (10 ) range, slow adsorption kinetics and competitive adsorption limit its application in analytical chemistry. 

X0 compounds are supported on oxide surfaces, again vibrational (Raman in particular) and optical spectroscopies provided significant information for structural assignments. OH groups, oxide ions and oxo-species may thus be considered as intrinsic probes. The characterization of anion vacancies (Lewis acid sites) can be performed using probe molecules (CO, NH3, pyridine, etc.). The use of model molecular compounds has almost completely been confined to their application as reference compounds (alcohols, carbonates, bicarbonates, carbonyls, carboxylates, Lewis acid-base adducts, 0x0-compounds, etc.) for the interpretation of spectroscopic data. 

---