Raman spectroscopy

raman In Raman spectroscopy (equivalent to Raman spectroscopy), a sample is irradiated with monochromatic light, which is usually a laser. Most of the radiation scattered by the sample will have the same frequency as the incident radiation - a process known as Rayleigh scattering. However, some of the radiation scattered by the sample, approximately one photon in ten million (0.000001%), will have a frequency offset from the frequency of the original laser radiation. Radiation with a higher wavelength is called the Stokes scattering component and has a lower energy than laser radiation. Vibrational states studied in Raman spectroscopy are the same as in IR spectroscopy. Raman and IR spectroscopy are essentially complementary, mutually complementary methods. Vibrations that are strongly manifested in the IR spectrum (strong dipoles) are usually weakly manifested in the Raman spectrum. At the same time, non-polar functional groups that give very intense Raman bands tend to give weak IR signals. For example, vibrations of hydroxyl, carbonyl or amino groups are very strong in the IR spectrum and very weak in the Raman spectrum. However, double and triple carbon-carbon bonds and symmetric vibrations of aromatic groups are very strong in the Raman spectrum. In this regard, Raman spectroscopy is used not only as a separate method, but also in combination with IR spectroscopy to obtain the most complete picture of the nature of the sample. Vibrational spectroscopy provides key information about the structure of molecules. For example, the position and intensity of bands in a spectrum can be used to study the molecular structure or chemical identification of a sample.

As a result of the analysis, one can identify chemical components (determine the nature of a substance) or study intramolecular interactions by observing the position and intensity of the bands in the Raman spectrum. Raman spectroscopy has significant advantages over other analytical methods. The most important of them are the simplicity of sample preparation and the large amount of information obtained. Raman spectroscopy is a light scattering technique, so all that is required to collect a spectrum is to direct the incident beam directly at the sample and then collect the scattered light. The sample thickness does not cause problems for Raman spectroscopy (in contrast to IR spectroscopy when analyzing samples for transmission), and the surrounding atmosphere makes an insignificant contribution to the Raman spectra. Therefore, there is no need to evacuate or dry the sample cell compartment. Glass, water, and plastic packaging themselves have very weak Raman spectra, which makes the method even easier to use. Often, samples can be analyzed directly in a glass bottle or plastic bag without opening the package and without the risk of contamination. The aqueous solutions are ready for analysis, there is no need to remove water to analyze the dissolved sample, and since atmospheric humidity is irrelevant, there is no need to purge the spectrometer. Moreover, there are no two molecules that have the same Raman spectra, and the intensity of the scattered light is related to the amount of matter. This makes it easy to obtain both quantitative and qualitative information about the sample, makes it possible to interpret the spectrum, process the data using computer methods of quantitative analysis. Raman spectroscopy is a non-destructive method of analysis. There is no need to dissolve solids, compress tablets, press the sample against optical elements, or otherwise change the physical or chemical structure of the sample. Thus, Raman spectroscopy is widely used to analyze physical properties such as crystallinity, phase transitions, and polymorphic states. Raman spectroscopy has several additional advantages over other vibrational methods, since the spectral range does not depend on the vibrational features under study. Other vibrational techniques require a set of frequencies that directly correspond to the frequencies of interest. Raman spectroscopy is the best choice for researchers because it works over a wide range from UV to NIR, allowing you to select the most convenient range for a given sample and obtain the best results. Raman spectroscopy allows the study of vibrational states associated with frequencies in the far infrared region, which are difficult to study with other methods.