Raman spectroscopy, general description

As described at the end of section Al.6.1. in nonlinear spectroscopy a polarization is created in the material which depends in a nonlinear way on the strength of the electric field. As we shall now see, the microscopic description of this nonlinear polarization involves multiple interactions of the material with the electric field. The multiple interactions in principle contain infomiation on both the ground electronic state and excited electronic state dynamics, and for a molecule in the presence of solvent, infomiation on the molecule-solvent interactions. Excellent general introductions to nonlinear spectroscopy may be found in [35, 36 and 37]. Raman spectroscopy, described at the end of the previous section, is also a nonlinear spectroscopy, in the sense that it involves more than one interaction of light with the material, but it is a pathological example since the second interaction is tlirough spontaneous emission and therefore not proportional to a driving field... 

Numerous published papers have dealt with infra-red and Raman spectroscopy of nitro compounds. A general description is given in the monograph by Bellamy [26] and more recent reviews by Rao [27] and for non-aromatic nitro compounds by Novikov and co-authors [7]. 

The algebraic approach begins with the notion of a zeroth-order description based on a dynamical symmetry, a concept which is a generalization of the usual definition of the symmetry group of the Hamiltonian. What a dynamical symmetry means in practice is that one constructs a zeroth-order Hamiltonian for which there is a full set of quantum numbers for labeling the eigenstates and that the energy is an analytical function of these quantum numbers. In the infrared or Raman spectroscopy of polyatomic molecules (1) one knows that to zeroth order it is practical to represent the spectrum by a Dunham-type formula... 

Classical, spontaneous Raman scattering is a powerful analytical tool that allows for the investigation of the qualitative and quantitative composition of biological, pharmaceutical, and environmental samples. The following discussion of NIR-Raman spectroscopy will begin with a general review of Raman spectroscopy, followed by a description of NIR-Raman, with further discussion about instrumentation and applications of the NIR-Raman technique. 

An excellent example of a complex sample is a living cell. Its measured Raman spectrum contains spectral features that correspond to each of the cell s biochemical components (DNA, proteins, carbohydrates, lipids, etc.). A description of the experimental methods used to acquire single-cell Raman spectra are given by Chan et al. [4] elsewhere in this book. For a general discussion of in vivo medical applications of Raman spectroscopy, we refer the reader to the excellent review article by Hanlon et al. [5]... 

To aid the general reader, short descriptions of the fundamentals of modern Raman scattering and attenuated total reflection (ATR) infrared spectroscopy are provided. This is followed for each spectroscopy by brief introductions to the enhancement mechanism involved. 

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