In order to overcome the limitations, special techniques are used to modify the classical Raman Spectroscopy. These non-classical Raman Spectroscopy includes: Resonance Raman Spectroscopy, surface enhanced Raman Spectroscopy, and nonlinear coherent Raman techniques, such as hyper Raman spectroscopy. The resonance effect is observed when the photon energy of the exciting laser beam is equal to the energy of the allowed electronic transition. Since only the allowed transition is affected, in terms of group theory, these are the totally symmetric vibrational ones.
As a result, RRS can increase the resolution of the classical Raman Spectroscopy, which makes the detection of dilution solution possible concentrations as low as 10 -3 M. RRS is extensively used for biological molecules because of its ability to selectively study the local environment. As an example, the Resonance Raman labels are used to study the biologically active sites on the bond ligand.
RRS can also be used to study the electronic excited state.
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- Raman Spectroscopy and its applications in Materials Science Part I.
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For example, the excitation profile which is the Raman intensity as a function of incident laser intensity can tell the interaction between the electronic states and the vibrational modes. Also, it can be used to measure the atomic displacement between the ground state and the excited state.
At , Fleischmann discovered that pyridine adsorbed onto silver electrodes showed enhanced Raman signals. Also, it is a better tool to study highly diluted solutions. In a nonlinear process, the output is not linearly proportional to its input. Since CARS signal is at anti-Stoke region a higher energy region than fluorescence , the influence of fluorescence is eliminated.
Thus, CARS is very useful for molecules with high fluorescence effect, for example, some biological molecules. High-resolution CARS has been developed as a tool for small-time scale process, such as photochemical analysis and chemical kinetics studies. Introduction Generally speaking, vibrational and rotational motions are unique for every molecule.
Despite the limitations above, Raman spectroscopy has some advantages over IR spectroscopy as follows: Raman Spectroscopy can be used in aqueous solutions while water can absorb the infrared light strongly and affect the IR spectrum. Because of the different selection rules, vibrations inactive in IR spectroscopy may be seen in Raman spectroscopy. This helps to complement IR spectroscopy. There is no destruction to the sample in Raman Spectroscopy. In IR spectroscopy, samples need to disperse in transparent matrix. For example grind the sample in solid KBr.
In RS, no such destructions are needed. Glass vials can be used in RS this should only work in the visible region. If in UV region, glass is not applicable because it can strongly absorb light too. Raman Spectroscopy needs relative short time. So we can do Raman Spectroscopy detection very quickly. Applications Raman Spectroscopy application in inorganic systems X-ray diffraction XRD has been developed into a standard method of determining structure of solids in inorganic systems.
Raman Spectroscopy Application in Organic Systems Unlike inorganic compounds, organic compounds have less elements mainly carbons, hydrogens and oxygens. Non-classical Raman Spectroscopy Although classical Raman Spectroscopy has been successfully applied in chemistry, this technique has some major limitations as follows: The probability for photon to undergo Raman Scattering is much lower than that of Rayleigh scattering, which causes low sensitivity of Raman Spectroscopy technique.
Thus, for low concentration samples, we have to choose other kinds of techniques. Journals Books Databases.
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