What Is Vibrational Raman Spectroscopy: A Vibrational or an Electronic Spectroscopic… DOI: http://dx.doi.org/10.5772/intechopen.86838

much larger than the Raman cross section, the Raman peaks typically ride on top of the spectrally broad fluorescence background so that it can be time-consuming to determine the true Raman intensity. Sometimes a part of the Raman spectrum may even be hidden behind the fluorescence. However, in most situations the influence from fluorescence may be taken care of by changing the laser wave number to NIR or to UV, by applying a fluorescence quenching technique [8], by applying a pulsed detection technique, or by implementing advanced signal processing including multivariate analysis.

In the present chapter vibrational Raman spectroscopy is discussed under the headline: "What is vibrational Raman spectroscopy: a vibrational or an electronic spectroscopic technique, or both?" Besides giving an answer to this question, the goal of the chapter is twofold: (1) to improve the readers' understanding of Raman scattering in general and (2) to demonstrate which kind of molecular information one may achieve by choosing different experimental conditions.

Before we begin the discussion, it should be noticed that Raman spectroscopy, like any kind of molecular spectroscopy, can be applied in two different ways: (1) as an analytical technique for the identification and quantification of molecules in a sample and (2) as a technique for studying the physical and chemical properties of molecules. In the first kind of application, the Raman signal is just considered as a source of data, which has to be compared with spectroscopic databases or which has to be combined with the chemometric method being most appropriate for the problem to be solved. For this kind of application, no knowledge of Raman theory and how the theory is applied to molecules is really needed. But it should be noticed that to decide how the chemometrics should be applied together with the Raman data, one must take into account that vibrational Raman spectra are in general characterized by exhibiting high spectral resolution (narrow and well-separated lines) compared to the broader bands typically found in IR and in particular in UV/ VIS spectra. For the second kind of applications, a deeper understanding of molecular physics and molecular Raman theory is needed.
