The ability to use quartz or Hi-grade Sapphire as a window material means that high pressure cells can be used to acquire Raman spectra of catalytic reactions. Integrated Platform. A notch or edge filter is used to eliminate Rayleigh and anti-Stokes scattering and the remaining Stokes scattered light is passed on to a dispersion element, typically a holographic grating. Transitions which have large Raman intensities often have weak IR intensities and vice versa. Raman Spectroscopy is a non-destructive chemical analysis technique which provides detailed information about chemical structure, phase and polymorphy, crystallinity and molecular interactions. Conversely, relatively neutral bonds (e.g. If the vibrational mode involved in the Raman scattering process is totally symmetric then the polarization of the Raman scattering will be the same as that of the incoming laser beam. After the scattering event, the sample is in a different rotational or vibrational state. Typically, a sample is illuminated with a laser beam. However, advances in software (like the 'Find Trends' feature in iC Raman 7) have enabled this expertise to be automated in a way that experts and non-experts alike can easily extract key information quickly for fast, confident decision making. A general introduction is given to the principles and theory of Raman spectroscopy, the discipline dealing with spectral analysis of inelastic scattering of light by the vibrating molecules in liquids, solids, or gases – the phenomenon called Raman scattering. The most common approach is hyperspectral imaging or chemical imaging, in which thousands of Raman spectra are acquired from all over the field of view by, for example, raster scanning of a focused laser beam through a sample. Raman spectroscopy offers several advantages for microscopic analysis. In solid state chemistry and the bio-pharmaceutical industry, Raman spectroscopy can be used to not only identify active pharmaceutical ingredients (APIs), but to identify their polymorphic forms, if more than one exist. Since that time, Raman has been utilized for a vast array of applications from medical diagnostics to material science and reaction analysis. The latter approach eliminates the possibility of sample stream contamination. Because vibrational frequencies are specific to a molecule's chemical bonds and symmetry (the fingerprint region of organic molecules is in the wavenumber range 500–1,500 cm−1), Raman provides a fingerprint to identify molecules. The name "Raman spectroscopy" typically refers to vibrational Raman using laser wavelengths which are not absorbed by the sample. Raman spectroscopy is a scattering technique. The photons that were scattered by the sample were collected through an optical flat at the end of the tube. As an example, molecules that contain bonds between homonuclear atoms such as carbon-carbon, sulfur-sulfur, and nitrogen-nitrogen bonds undergo a change in polarizability when photons interact with them. This excitation puts the molecule into a virtual energy state for a short time before the photon is emitted. Here ρ  However, the intensity of Raman scattering at long wavelengths is low (owing to the ω4 dependence of Raman scattering intensity), leading to long acquisition times. These products exploit the varied properties of silicone rubbers such as strength, thermal resistivity and stability. This issue often can be alleviated by using a longer wavelength excitation source. ), which can lend insight into the corrosive environments experienced by the artifacts. In a molecule that contains a center of inversion, Raman bands and IR bands are mutually exclusive, i.e.  Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. Polarization dependence of Raman scattering, Characterization of the symmetry of a vibrational mode, Spontaneous (or far-field) Raman spectroscopy, Enhanced (or near-field) Raman spectroscopy, Howell G. M. Edwards, John M. 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Now, Raman spectroscopy has become one of the most popular approaches to study the vibrational structures of molecules together with infrared spectrum. Distributed temperature sensing (DTS) uses the Raman-shifted backscatter from laser pulses to determine the temperature along optical fibers. Although some vibra-tions may be active in both Raman and IR, these two forms of spectroscopy arise from different processes and different selection rules. For example, the drug Cayston (aztreonam), marketed by Gilead Sciences for cystic fibrosis, can be identified and characterized by IR and Raman spectroscopy. This introduction gives you an overview of the theory of Raman spectroscopy and an introduction to the primary components of a Raman spectrometer. If the final state is higher in energy than the initial state, the scattered photon will be shifted to a lower frequency (lower energy) so that the total energy remains the same. The orientation of an anisotropic crystal can be found from the polarization of Raman-scattered light with respect to the crystal and the polarization of the laser light, if the crystal structure’s point group is known. ), Examination of particles in solution is important, e.g. There are many other variations of Raman spectroscopy including surface-enhanced Raman, resonance Raman, tip-enhanced Raman, polarized Raman, stimulated Raman, transmission Raman, spatially-offset Raman, and hyper Raman. Raman spectroscopy has been used in several research projects as a means to detect explosives from a safe distance using laser beams. The shorter wavelength lasers have higher Raman scattering cross-sections so the resulting signal is greater, however the incidence of fluorescence also increases at shorter wavelength. In the classical wave interpretation, light is considered as electromagnetic radiation, which contains an oscillating electric field that interacts with a molecule through its polarizability. Because the laser light does not excite the molecule there can be no real transition between energy levels. Theory of Raman Scattering When considering Raman scattering, we can think about the physics in one of two ways: the classical wave interpretation or the quantum particle interpretation.  Raman won the Nobel Prize in Physics in 1930 for this discovery. Learn the basic theory behind normal, resonant, and surface-enhanced Raman scattering. Raman spectroscopy is used in chemistry to identify molecules and study chemical bonding and intramolecular bonds. , It is capable of identifying individual pigments in paintings and their degradation products, which can provide insight into the working method of an artist in addition to aiding in authentication of paintings. 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