**1. Introduction**

The vibrational spectroscopies have been largely employed in the determination of the molecular structure and played a central role in many areas, from fundamental chemistry to materials engineering. Among these techniques, the Raman spectroscopy is essential today in the study of nanostructured materials and biological systems in *in situ* and *in vivo* conditions. In addition, by intensification process, very small quantities can be analyzed (for certain cases in the limit of single molecule regime). Detailed information about the molecular structure can be obtained, because each vibration of atoms shows a characteristic position and intensity. Both position and intensity are influenced by the chemical environment, or in other words by chemical bonds, inter- and intramolecular forces.
