Do you know RAMAN spectroscopy? I will give you a brief summary of what this effect is about.
Hello friends I hope you are great, today I return with a very interesting publication, it is a very important technique and used by experimental physicists to determine the spectra of various materials, it is raman spectroscopy and then I will explain a brief summary about it.
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Raman spectroscopy is a technique widely used to identify different materials, be it semiconductors, solid materials, liquid substances, among others. It could be said that the result of the spectroscopy made to any compound, has been its fingerprint or identification card, to put it in a vulgar and not scientific way. and what makes it different from the techniques that I explained earlier. It is a technique that is performed directly on the material without the need to prepare the sample before measuring it or performing the sweep, there is no need to submit the sample to a chemical or physical treatment.
In this technique one of its main uses in the physics of the solid state is to determine the vibrational modes of the crystalline network, that is to say the low frequency modes, also the rotary modes, all of which provides us with an important information about the structure of a material.
Raman spectroscopy can be used for both qualitative and quantitative applications. The spectra are very specific, and chemical identifications can be made through the use of search algorithms in digital databases. As in infrared spectroscopy, the band areas are proportional to the concentration, which makes Raman susceptible to quantitative analysis. In fact, because Raman bands are intrinsically sharper than their infrared counterparts, isolated bands are often present in the spectrum for more direct quantitative analysis.
The branch spectroscopy uses a monochromatic laser light source to influence the sample in order to generate a spectrum where the Raman effect can be visualized, using a detector camera. This light generates a characteristic spectral pattern of a material and allows in turn to identify substances that evaluate and determine the vibrations, crystallinity and orientation of the low frequency modes.
Sir CV Raman
Sir Chandrasekhara Venkata Raman was an Indian physicist whose main work was very important for the scientific community, especially physics. In 1928 together with another physicist K.S. Krishman discovered the Raman effect, which confirmed the quantum nature of light. The following year he was appointed by the British crown Sir. He received the Nobel Prize in Physics in 1930 for the discovery that when light passes through a transparent material, part of the diffracted light changes its wavelength. This phenomenon is currently known as Raman scattering and is the result of the Raman effect. In addition, in 1932, he discovered the spin of the quantum photon together with Bhagavantam, he also worked on the acoustics of musical instruments and with his student Nagendranath they came to the theoretical explanation of the optical-acoustic effect (dispersion of light by sound waves) in the Raman-Nath theory.
After its discovery, the Raman effect became the technique preferred by many scientists for the analysis of infrared absorption spectroscopy, however by that time the technique, although very effective for such analyzes, was complex and needed personnel. trained to calibrate and assemble the necessary equipment to perform the characterization of compounds, this staff had to use very consistent equipment in mercury lamps, spectrographs or photographic films to obtain the spectra.
Scheme of the depersive energy of the Raman spectrum.
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As the years passed and the technique was perfected, it undoubtedly became the number and in 1960 it was very close to experiencing great advances since with the appearance of the laser, which replaced the mercury lamp and later the development of fiber optics in the 80s, the technique was acquiring the appropriate perfection and the spectra were increasingly observed with better quality and sharpness, and then in the 90s came out the filters, gratings or diffraction gratings and the CCDs and converted this spectroscopy in the best technology, the most powerful and easy to use, it should be noted that there are currently portable equipment easy to handle and assemble.
Now the basic mechanisms on which raman spectroscopy is based are the following:
When we obtain the Raman spectra, three types of dispersion are observed. The first one is the Rayleigh line, which consists of an electromagnetic radiation falling on a molecule, this is a pass to a next level or scale, after losing this excitement. The molecule returns to the level where it starts, this means that no variation in the energy is observed and therefore the incident and scattered radiation has the same wavelength and frequency.
The Stokes lines, the process is very similar to that of the Rayleigh lines, but the difference is that the molecule that loses excitation permances in a state or vibrational level higher than the initial one and this brings as immediate consequence the absorption of the wavelength and the dispersion of another, that is, they have gained energy and present less frequency.
And finally the anti-Stokes lines, in this mechanism presents the same as the Stokes lines, but in this case the only difference is that the molecule returns to a lower level and this produces that the scattered radiation is greater than the absorbed and the frequency therefore it is greater.
Diagram of Raman energy dispersive levels.
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What is the Phenomenon (dispersion or raman effect).
When light is scattered by matter, almost all dispersion is an elastic process (Rayleigh scattering) and there is no change in energy. However, a very small percentage of dispersion is an inelastic process, therefore, a scattered light has energy different from the incident light. This inelastic scattering of light was predicted theoretically by Adolf Smekal in 1923 and first observed experimentally by Chandrasekhara Venkata Raman in 1928, which is why this inelastic scattering is called Raman scattering (Raman effect).
Diagram of the process that occurs in the dispersive energy Raman.
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Then we could say as mentioned at the beginning of the publication that if we incise a monochromatic beam of light, that is to say a laser, on the material to be characterized, a certain part of the light is scattered and has the same frequency as the wave that hits the material . Another portion of the light is dispersed inelastic and returns the frequency of each molecule that makes up the material, this phenomenon is known as the Raman effect.
We can observe in this phenomenon that the variations in the frequency are caused by variations of the energy between the bonds of the molecules, each link could be said to be a door that unites both masses, that when excited by the beam of light produces vibrational movements and rotational at a specific frequency of each link. That is why each of the movements of molecules corresponds to a given energy value. The type of inelastic dispersion are distinguished in both cases, however, if the dispersed photon has a lower energy than the incidence, Stokes scattering occurs, and conversely, if the energy is greater, Anti-Stokes dispersion occurs.
This figure presents a model of atoms linked by a gate or spring of both masses of the molecules.
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The references with which support was given to the writing of the post are linked to the images.
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