Cross section for Raman scattering

The more conventional, energy domain fonnula for resonance Raman scattering is the expression by Kramers-Heisenberg-Dirac (KHD). The differential cross section for Raman scattering into a solid angle dD can be written in the fomi... 

We have seen that the strength of Raman scattered radiation is directly related to the Raman scattering cross-section (Oj ). The fact that this cross-section for Raman scattering is typically much weaker than that for absorption (oj limits conventional SR as a sensitive analytical tool compared to (Imear) absorption... 

The metal substrate evidently affords a huge ( 10 and even as high as 10 [84, 85]) increase in the cross-section for Raman scattering of the adsorbate. There are two broad classes of mechanisms which are said to contribute to this enhancenient [, and Ml- The first is based on electromagnetic effects and the second on cheniicaT effects. Of these two classes the fomier is better understood and, for the most part, the specific mechanisms are agreed upon the latter is more complicated and is less well understood. SERS enhancenient can take place in either physisorbed or chemisorbed situations, with the chemisorbed case typically characterized by larger Raman frequency shifts from the bulk phase. 

Surface-enhanced Raman scattering is a phenomenon where the cross section for Raman scattering for molecules adsorbed on some surfaces is enhanced by many orders of magnitude compared to the scattering cross section for the same molecule in the bulk—in solution, for example. 

In resonance Raman experiments it is very important to consider the effect of the absorbed light on the sample composition. Raman scattering and absorption are independent events. Some photons are scattered, but a much larger number are absorbed. Cross sections for Raman scattering are on the order of 10" A /molecule, whereas cross sections for absorption are about 1 A /molecule. Thus, if photon absorption results in a photochemical transformation, as in the case of visual pigments, the effect of the photoalteration must be carefully considered. This situation has been analyzed in detail and rapid-flow methods devised that allow one to obtain resonance Raman spectra of even the most photolabile molecules without distortion of the sample composition. " ... 

In addition to DNA and RNA large amounts of associated proteins known as histones, as well as other proteins, are present in the chromosomes. The relatively low cross-section for Raman scattering of chromosomes is the reason for the lack of normal Raman investigations. Recently, the first Raman spectra of intact chromosomes... 

As this review is primarily concerned with low-energy electronic scattering in the normal and superconducting states of high-rc superconductors, it is useful to consider in detail the cross-section for Raman scattering from intraband electronic excitations. Using eqs. (6) and (7), the electronic Raman scattering cross-section can be related to a correlation function associated with an effective density p. 

Because the cross-sections for Raman scattering are extremely small, it is used in lidar only for a few, specific applications due to its limited range and sensitivity (for one of those applications see the segment on stratospheric studies further below). 

FT-Raman spectroscopy does have some disadvantages, as might be expected. The cross section for Raman scattering at the IR excitation wavelength of 1.06 p,m is... 

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