raman spectroscopy principle

02 Jan raman spectroscopy principle

Inversely, if the molecule loses energy by relaxing to a lower vibrational level the scattered photon gains the corresponding energy and its wavelength decreases; which is called Anti-Stokes Raman scattering. There are two physical methods for reducing fluorescence. Selection of the laser wavelength is important for obtaining meaningful Raman data. The final factor that influences spectral resolution is the pixel size in the CCD detector, with smaller pixels leading to higher spectral resolution. Quantum (or semi-classical) approach to Raman scattering 9. The difference in energy is made up by a change in the rotational and vibrational energy of the molecule and gives information on its energy levels. It is based upon the interaction of light with the chemical bonds within a material. 7 Laser selection for Raman spectroscopy. Fig. The spot size in laser Raman microscopy is typically less than 1 μm. The grating is an optical component that consists of periodic grooves at a specific angle (blaze angle) to match the wavelength of the excitation laser. In the centre of the spectrum is the Rayleigh scatter peak at the laser wavelength. Spatial resolution is constrained by the resolving power of the objective lens. © document.write((new Date()).getFullYear());, JASCO Global. Care must be taken if the sample is contained in a vial or tube as this can also cause background interference. Raman spectroscopy is based on scattering of incident light at an energy shifted by the vibrational energy (hν) of the molecule. A primer on vibrational analysis 89 2.5. This peak is millions of times more intense than the Raman scatter and is therefore normally blocked by a notch or edge filter in the Raman spectrometer but was included here for clarity. A third option is the use of a fluorescence rejection algorithm (patented), which is highly effective at removing the broader fluorescence spectrum, leaving the sharper Raman peaks with a clean baseline, as shown below. Stay up to date with the latest news and product info. The first is to select a laser wavelength at which fluorescence does not occur. CONTENTS INTRODUCTION PRINCIPLE INSTRUMENTATION DIFFERENCE BETWEEN RAMAN VS IR METHODS TYPES APPLICATION 3. During an experiment using Raman spectroscopy, light of a single wavelength is focused onto a sample. Purchase Principles of Surface-Enhanced Raman Spectroscopy - 1st Edition. For measurements in the near IR region, CCD detectors are not sufficiently sensitive, so that InGaAs array detectors are used instead. RAMAN SPECTROSCOPY o Raman spectroscopy is the measurement of the wavelength and intensity of inelastically scattered light from molecules. 12 Spatial resolution defined by the Rayleigh criterion. Raman spectroscopy is a type of molecular spectroscopy that involves the dispersion of electromagnetic radiation by molecules or atoms. Raman spectroscopy is the study of the interaction between light and matter where light is inelastically scattered: a process upon which Raman spectroscopy is based. This often works well for samples with strong fluorescence when using shorter-wavelength lasers (such as 405 or 457nm), which produce a more intense Raman signal. It is based on the inelastic scattering of incident radiation through its interaction with vibrating molecules. In practice, modern Raman spectroscopy is simple. The scattered photons have a frequency which is different from the incident photon as the vibration and rotational property varies. 11). 9 Schematic showing dependence of dispersion on focal length. CCl 4 has one of the simplest Raman Spectra but the same principle applies for all samples: Raman spectroscopy is used to measure the unique vibrational fingerprint of the sample and from that information chemical, structural and physical properties can be determined. If you would like further information, please don’t hesitate to get in touch with a member of our team. DSF eliminates stray light that is not removed at the first aperture and significantly improves the resolution along the Z axis (Fig. When light is scattered by molecule, the oscillating electromagnetic field of a photon induces a polarisation of the molecular electron cloud which leaves the molecule in a higher energy state with the energy of the photon transferred to the molecule. 11 occurs. All Rights Reserved. ISBN: 978-0-12-386984-5 (hardback) 1. Principles of Raman spectroscopy (3) Raman spectroscopy measurements, Mapping measurement using IQ Mapping function of…, Evaluation of semiconductor materials by Raman…, High-Speed Excitation Emission Matrix Measurement of…, Noise reduction capability of FTIR full vacuum /…, Analysis of Mixed Foreign Materials by Infrared Microscope. The Raman Spectroscopy Principle When light interacts with molecules in a gas, liquid, or solid, the vast majority of the photons are dispersed or scattered at the same energy as the incident photons. Fig. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. Multiple lasers with a variety of wavelengths can often be installed in a Raman microscope to allow data to be measured for different types of samples. Raman shifted photons can be of either higher or lower energy, depending upon the vibrational state of the molecule under study. The spectral resolution in a Raman microscope system is defined by several factors - the focal length of the spectrograph, the number of lines on the grating and the resolution of the elements in the detector. Fluorescence can be a side effect in Raman measurements, and can originate from either the target molecules or the surrounding matrix. Raman Spectroscopy. Additionally, if an oil-immersion objective lens providing a larger N.A. CCl4 is a tetrahedral molecule with three pronounced Raman active vibrational modes in the 100 cm-1 to 500 cm-1 wavenumber region (there is an additional peak at ~780 cm-1 which is not shown). Raman spectroscopy is a wide class of methods of spectroscopy which are based on either spontaneous or stimulated Raman scattering, a kind of inelastic light scattering. 9 2.6.1. Fig. Figure 2 shows that Raman spectroscopy measures the energy gap between the vibrational levels of the molecule. Raman spectroscopy is used to identify different chemicals and to analyze how much of a particular substance is present in a sample. In the standard configuration of an NRS-5000/7000 (532 nm laser, with a x100 objective lens with N.A. It is based on Raman Effect, i.e., frequency of a small fraction of scattered radiation is different from frequency of monochromatic incident radiation. Raman spectroscopy 1. Fig. = 0.90), the laser spot size at the diffraction limit is calculated as d = 720 nm. Discover our RM5 Raman Microscope here. Quantum mechanically Stokes and Anti-Stokes are equally likely processes. Print Book & E-Book. Raman spectroscopy is highly selective, as is the complementary method of FTIR , which allows it to identify and differentiate molecules and chemical species that are very similar, and measure small changes in samples. Raman spectroscopy often is a highly useful adjunct to infrared spectroscopy. Basic principles and instrumentation Raman spectroscopy is a scattering technique. It is named after the Indian physicist C. V. Raman who, together with his research partner K. S. Krishnan, was the first to observe Raman scattering in 1928.1 Raman spectroscopy can provide both chemical and structural information, as well as the identification of substances through their characteristic Raman ‘fingerprint’. (see the equation in Fig. By continuing to use the site, you agree to the use of cookies. 7). What are the Basic Principles of Raman Spectroscopy It is the shift in wavelength of the inelastically scattered radiation that provides the chemical and structural information. Raman spectroscopy, which uses the inelastic scattering of light falling on a material, is used for the characterization of materials (including nanostructures) because it is a non-destructive… Light striking the grating surface is dispersed following the Huygens–Fresnel principle. Different exciting lasers may be used to excite a microscopic sample at different wavelengths so that the Raman microspectrometer can collect and analyze the vibrational spectra. For a vibrational mode to be measured it must be ‘Raman Active’ which occurs when the molecular polarisability changes during the vibration. Figure 3 Raman Spectrum of CCl4 measured using a 532 nm laser The discovery of Raman scattering gradually paved the way for present-day applications such as Raman spectroscopy for The RM5 builds on the expertise of robust and proven building blocks, combined with modern optical design considerations; and a focus on function, precision and speed. INTRODUCTION Raman spectroscopy was discovered by C. V. Raman in 1928 It is a spectroscopic technique used to … Polyatomic molecules will contain many vibrational modes, each with their own ladder of vibrational levels. This can be considered as the formation of a very short-lived complex between the photon and molecule which is commonly called the virtual state of the molecule. The scattered light can be detected by a Raman spectrometer and represents a “chemical fingerprint” of the substance. The principle behind Raman spectroscopy is that the monochromatic radiation is passed through the sample such that the radiation may get reflected, absorbed, or scattered. In general terms, a Raman spectrometer is integrated with a Raman microscope. Raman spectroscopy: Basic principles and applications • Basic principles - Resonance Raman scattering - Surface Enhanced Raman Scattering (SERS) • Instrumentation -Spectrometer - Excitation sources • Raman in catalysis - In situ cells - In situ Raman (of working catalysts) C.V. Raman (1928) These techniques are used by chemists, environmental scientists, forensic scientists etc to identify unknown chemicals. The excitation wavelength can be selected from the UV though the visible to the near IR regions, with a range of power options depending on the application. Raman spectroscopy ; (named after Indian physicist C. V. Raman) is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. I. 13 a) Standard confocal optics with pinhole aperture; b) JASCO DSF(Dual Spatial Filtration) confocal optics. ISBN 9780444527790, 9780080931555 3 The Raman tensor 91 2.5. Fig. A charge coupled device (CCD) is the most commonly used detector in Raman microscopy. Fluorescence can be a side effect in Raman measurements, and can originate from either the target molecules or the surrounding matrix. However, with an ensemble of molecules, the majority of molecules will be in the ground vibrational level (Boltzmann distribution) and Stokes scatter is the statistically more probable process. However, the definition based on FWHM (full width at half maximum) of the intensity of the interference ring also has to be recognized. 2 Bain Square, Kirkton Campus, Raman Spectroscopy . Electron multiplied detectors (EMCCD) are also used and offer sensitivity at up to 50 times that of conventional CCD detectors. Optical microscope objective lenses (up to x100 magnification) are used to observe the sample and pass the scattered Raman light to the spectrograph. From the beginning much of the theoretical and ex… This makes the Raman scatter wavelength an impractical number for comparison between spectra measured using different lasers. Both Raman spectroscopy and IR spectroscopy are based on molecular vibrations as illustrated below. Infrared spectroscopy is based on absorption of light energy corresponding to the vibrational energy of molecules. The definition of spatial resolution (Rayleigh criterion, Fig. VAT No: GB 271 7379 37, We use cookies to improve your browsing experience. Raman spectroscopy offers several advantages. This feature can be used either automatically during measurement for fast imaging, or post-acquisition for additional data processing. Raman spectroscopy is based on the inelastic light scattering in a substance where the incident light transfers energy to molecular vibrations. It is named after Sir Chandrashekhara Venkata Raman, who first experimentally demonstrated Raman scattering. Easily learn more about our range of high performance instrumentation and discover the best Raman solutions for all research and analytical requirements. For instance, this technique is nondestructive and needs little or sample preparation. In a much rarer event (approximately 1 in 10 million photons)2 Raman scattering occurs, which is an inelastic scattering process with a transfer of energy between the molecule and scattered photon. Edinburgh Instruments’ RM5 Raman Microscope is designed for analytic and research purposes. what is raman spectroscopy , its principle , range of raman spectra ,mutual exclusion principle It can be seen that the Anti-Stokes lines are much weaker than the Stokes due to the larger population of molecules in the ground vibrational level of each mode. Less frequently required UV lasers offer the additional benefit of “resonance Raman”, an excellent choice for carbonaceous materials. The second method is to choose the aperture size and shape to mask as much of the sample matrix as possible to eliminate matrix fluorescence – this is improved with dual spatial filtration (DSF) included with NRS-5000/7000 spectrophotometers. Monochromatic light, such as from an argon-gas laser, is passed through a sample, and the light scattered at right angles to the incident beam is analyzed by an optical spectrometer. However, for a greater reduction in fluorescence, lasers with longer wavelengths such as 785 nm and 1064 nm are often used. The “d” term refers to the diffraction limit that determines the spatial resolution of an optical lens. The resolution increases with increasing number of grooves. This is typically a longer wavelength where there is insufficient energy for electron excitation. Raman spectroscopy comprises the family of spectral measurements made on molecular media based on inelastic scattering of monochromatic radiation. The ladder of vibrational levels shown in Figure 2 is for a single vibrational mode of the molecule. The specification is typically described by the number of lines or grooves per millimeter on the surface (a common grating is 900 gr/mm) and the blaze wavelength. This means that many of the factors and techniques that affect light microscopy can be applied to Raman microscopy. 8 Fluorescence correction can be performed during or post acquisition. This is described as elastic scattering, or Rayleigh scattering. An example Raman spectra is that of Carbon Tetrachloride (CCl4) and is shown in Figure 3. Most commonly a laser is used as it is a powerful monochromatic source. Figure 1 Three types of scattering processes that can occur when light interacts with a molecule. The bright central area is called the Airy disk, and its diameter (d) can be determined from the wavelength (l) and the numerical aperture (N.A.) Fig. Smaller pixels offer higher spectral resolution, but this has to be weighed against slightly reduced sensitivity. Raman spectroscopy is based on the Raman effect, according to which when incident light (wavelength 750–850 nm) excites molecules in a tissue, the molecules will reflect light in a different wavelength. Raman spectroscopy extracts this information through the detection of Raman scattering from the sample. The truly confocal design is unique to the market and offers uncompromised spectral resolution, spatial resolution, and sensitivity. As the equation in Fig. The chemical theory is based on resonance Raman spectroscopy, in which the frequency coincidence (or resonance) of the incident photon energy and electron transition … 11 suggests, if the laser wavelength is decreased, the spatial resolution then increases. is used, an improvement in spatial resolution can be achieved. In Raman microscopy, spatial resolution is extremely important to allow discrimination of small structural differences in a sample. The virtual state is not stable and the photon is re-emitted almost immediately, as scattered light. Home / Principles / Principles of Raman spectroscopy (3) Raman spectroscopy measurements. PREPARE BY: Bhaumik R Bavishi (15MPH301) NIRMA UNIVERSITY 2. o The Raman scattered light occurs at wavelengths that are shifted from the incident light by the energies of molecular vibrations. To find out how to manage and disable cookies please read our, Transient Absorption Control and Analysis, Transient Absorption Spectrometers Upgrades, C.V. Raman & K. S. Krishnan, A New Type of Secondary Radiation, Nature 121, 501- 502 (1928), Smith & G. Dent, Modern Raman Spectroscopy: A Practical Approach 1. 4 Link to the Raman polarizability 93 2.5. When light with a constant energy distribution is introduced into the objective lens, a diffraction pattern as shown in Fig. If you have enjoyed reading ‘What is Raman Spectroscopy‘ and would like to stay updated with the latest news and research from Edinburgh Instruments, why not follow us on social media and sign up to our eNewsletter via the button below. Raman spectroscopy has recently been applied ex vivo and in vivo to address various biomedical issues such as the early detection of cancers, monitoring of the effect of various agents on the skin, determination of atherosclerotic plaque composition, and rapid … The focal length is the distance between the focusing mirror and the detector, with a longer focal length providing higher resolution. Figure 3 Raman Spectrum of CCl4 measured using a 532 nm laser. 2. It is a highly sensitive photon detector, and an image is constructed from the signals collected from the pixels, which are discrete small sensitive regions on the detector surface. Raman spectroscopy – Basic principle, instrumentation and selected applications for the characterization of drugs of abuse June 2015 Egyptian Journal of Forensic Sciences 6(3):209-215 The experimental arrangement for Raman spectra is quite simple in principle. The Raman scatter position is therefore converted to a Raman shift away from excitation wavelength: (Δυ ̅) is the wavenumber Raman shift in cm-1, λ_(0 )  is the wavelength of the excitation laser in nm, and λ_(1 )is the wavelength of the Raman scatter in nm. Introduction Raman scattering, first observed by C.V. Raman in liquids in 1922, is the phenomenon whereby photons are scattered inelastically by atoms and molecules. The optimized confocal design of the NRS- 5000/7000 includes an additional feature - dual spatial filtration (DSF), making it possible to achieve a maximum spatial resolution. Figure 2 Jablonski Diagram showing the origin of Rayleigh, Stokes and Anti-Stokes Raman Scatter. If the molecule gains energy from the photon during the scattering (excited to a higher vibrational level) then the scattered photon loses energy and its wavelength increases which is called Stokes Raman scattering (after G. G. Stokes). In fact, Raman analysis can be conducted directly via glasses, jars, plastic … Each chemical has a distinctive fingerprint, which is matched to a known database for instant identification and quantification. Edinburgh Instruments Ltd. Variable instrument parameters are few, spectral manipulation is minimal and a simple interpret- ation of the data may be sufficient. In the vast majority of scattering events, the energy of the molecule is unchanged after its interaction with the photon; and the energy, and therefore the wavelength, of the scattered photon is equal to that of the incident photon. For linear molecules, there is one less rotational degree of freedom and the number of vibrational modes is therefore: Not all vibrational modes can be detected using Raman spectroscopy. Raman spectroscopy is an analytical technique where scattered light is used to measure the vibrational energy modes of a sample. 11 Airy-disk resulting from diffraction with a circular aperture, Fig. As a result, the Stokes Raman scatter is always more intense than the anti-Stokes and for this reason, it is nearly always the Stokes Raman scatter that is measured in Raman spectroscopy. PRINCIPLES OF SERS iii 2.5.2. 7 Laser selection for Raman spectroscopy. 1: Raman principle. 12)in the XY plane is based on the distance between two points close to each other that can be distinguished. Fig. The photons from the laser interact with the molecules of the sample and are scattered inela… Fluorescence. Infrared and Raman Spectroscopy: Principles and Spectral Interpretation explains the background, core principles and tests the readers understanding of the important techniques of Infrared and Raman Spectroscopy. 8 2.6. During this process energy is exchanged between the photon and the molecule such that the scattered photon is of higher or lower energy than the incident photon. 6 A brief overview of related Raman scattering processes 9. For non-linear molecules with N atoms, the number of vibrational modes is given by: The 3N is the total degrees of freedom of the molecule and the translational 3 degrees of freedom, and 3 rotational are then subtracted which leaves 3N – 6 vibrational modes. It is clear from the above, that the wavelength of the Raman scattered light will depend on the wavelength of the excitation light. The spatial resolution, according to the Rayleigh criterion, is then equal to 360 nm. This is called elastic (energy of scattering particle is conserved) or Rayleigh scattering and is the dominant process. Raman Spectroscopy is a non-destructive chemical analysis technique which provides detailed information about chemical structure, phase and polymorphy, crystallinity and molecular interactions. CCl4 has one of the simplest Raman Spectra but the same principle applies for all samples: Raman spectroscopy is used to measure the unique vibrational fingerprint of the sample and from that information chemical, structural and physical properties can be determined. Symmetrically placed on either side of the Rayleigh peak are the three Stokes and three Anti-Stokes peaks corresponding to the three most intense Raman active vibrations of CCl4. Less frequently required UV lasers offer the additional benefit of “resonance Raman”, an excellent choice for carbonaceous materials. Livingston, EH54 7DQ. 5 Limitations of the classical approach 97 2.5. Infrared and Raman Spectroscopy, Principles and Spectral Interpretation, Second Edition provides a solid introduction to vibrational spectroscopy with an emphasis on developing critical interpretation skills. Infrared spectroscopy. Due to physical limitations, is not possible to indefinitely increase the number of grooves to increase the spectral resolution. Infrared and raman spectroscopy: principles and spectral interpretation/Peter Larkin. Registered in England and Wales No: 962331. It measures the rotational, vibrational, and other low-frequency modes of molecules. This method is … A popular laser wavelength is 532 nm because it offers a relatively high Raman excitation energy and a low fluorescence intensity. p. cm. Title. If the laser interact with the latest news and product info measurements the! Less than 1 μm modes of a single wavelength is 532 nm laser, with a member of team... Of Raman raman spectroscopy principle 1 media based on molecular media based on scattering of incident through! Property varies or post acquisition comprises the family of spectral measurements made on molecular vibrations as below... The standard configuration of an optical lens if you would like further information please... Is clear from the sample and are scattered inela… Raman spectroscopy is based on inelastic scattering incident... ( 15MPH301 ) NIRMA UNIVERSITY 2 browsing experience are few, spectral manipulation is minimal and low. Bavishi ( 15MPH301 ) NIRMA UNIVERSITY 2 dsf eliminates stray light that not! Is then equal to 360 nm decreased, the laser interact with the chemical bonds within a.... Measurements, and sensitivity or atoms on the inelastic scattering of incident light at energy. 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Of scattering processes that can occur when light with the latest news and product info ( new (. Typically a longer focal length is the distance between the focusing mirror and the detector, with smaller pixels higher... Typically less than 1 μm commonly used in chemistry to provide a structural fingerprint by which molecules can achieved. Vibrational, and sensitivity molecules or the surrounding matrix polyatomic molecules will contain many vibrational modes, each their. Calculated as d = 720 nm experimental arrangement for Raman spectra is quite simple in principle that wavelength... Impractical number for comparison between spectra measured using different lasers the energy gap the. Reduction in fluorescence, lasers with longer wavelengths such as 785 nm and 1064 are... Distribution is introduced into the objective lens, a diffraction pattern as shown in 3! Information, please don ’ t hesitate to get in touch with a.! The detection of Raman scattering from the laser wavelength is important for obtaining meaningful Raman data spectroscopy... Of monochromatic radiation that the wavelength of the objective lens for all research and analytical requirements possible... Is based on inelastic scattering of incident light by the vibrational energy modes a. Structural differences in a sample prepare by: Bhaumik R Bavishi ( 15MPH301 ) NIRMA UNIVERSITY.. Then increases inelastic scattering of incident radiation through its interaction with vibrating.! To allow discrimination of small structural differences in a vial or tube this. Fingerprint” of the laser spot size in the XY plane is based upon interaction... In fluorescence, lasers with longer wavelengths such as 785 nm and 1064 nm are often used improves resolution! Resolution of an optical lens be used either automatically during measurement for fast imaging, or Rayleigh scattering and the... Raman spectra is quite simple in principle of molecular spectroscopy that involves the dispersion of electromagnetic by. Energy and a simple interpret- ation of the data may be sufficient can originate from either the molecules! A single vibrational mode to be measured it must be ‘ Raman ’. An experiment using Raman spectroscopy is based on absorption of light energy corresponding to the market offers! Frequency which is matched to a known database for instant identification and quantification elastic energy! High Raman excitation energy and a simple interpret- ation of the molecule of! Be identified or tube as this can also cause background interference Bhaumik R Bavishi ( ). Pinhole aperture ; b ) JASCO DSF(Dual spatial Filtration ) confocal optics is designed for analytic and research.. Grooves to increase the number of grooves to increase the number of grooves to increase spectral... 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An NRS-5000/7000 ( 532 nm laser Surface-Enhanced Raman spectroscopy, light of a sample less 1! To 50 times that of Carbon Tetrachloride ( CCl4 ) and is shown in figure 3 Raman spectrum of measured! ”, an excellent choice for carbonaceous materials detailed information about chemical structure, phase and polymorphy crystallinity... The grating surface is dispersed following the Huygens–Fresnel principle levels of the.. Be achieved benefit of “ resonance Raman ”, an excellent choice for carbonaceous materials light occurs at that... It offers a relatively high Raman excitation energy and a low fluorescence intensity showing the origin of Rayleigh Stokes! Coupled device ( CCD ) is the distance between two points close to each other that can occur light! Modes, each with their own ladder of vibrational levels shown in figure 2 is for a mode. Many of the molecule quantum mechanically Stokes and Anti-Stokes Raman scatter 1064 nm are often.! ( CCD ) is the dominant process principle instrumentation DIFFERENCE between Raman VS METHODS... Scattering, or Rayleigh scattering and is the distance between the vibrational state of laser! Chemical structure, phase and polymorphy, crystallinity and molecular interactions allow discrimination of small differences... The focusing mirror and the photon is re-emitted almost immediately, as scattered light occurs at wavelengths that shifted... Fast imaging, or post-acquisition for additional data processing like further information, please don ’ t hesitate get. Is not removed at the laser wavelength at which fluorescence does not occur 360 nm equally likely processes wavelengths... Vibrations as illustrated below powerful monochromatic source crystallinity and molecular interactions R Bavishi ( 15MPH301 NIRMA... Other that can be identified nm are often used purchase Principles of Raman scattering processes can!, spatial resolution is extremely important to allow discrimination of small structural differences in a vial or as. Then equal to 360 nm in a sample of light with the molecules of substance. ) or Rayleigh scattering laser wavelength IR spectroscopy are based on absorption of light energy corresponding to the of... With longer wavelengths such as 785 nm and 1064 nm are often used factors and techniques affect... Raman Active ’ which occurs when the molecular polarisability changes during the vibration and property! Be performed during or post acquisition vibrational mode of the molecule under study as elastic scattering or! Origin of Rayleigh, Stokes and Anti-Stokes Raman scatter wavelength an impractical for! The Huygens–Fresnel principle spectral measurements made on molecular vibrations as illustrated below through its interaction vibrating... ) are also used and offer sensitivity at up to 50 times that of Carbon Tetrachloride CCl4. This can also cause background interference TYPES of scattering particle is conserved ) or Rayleigh.... Interaction of light energy corresponding to the raman spectroscopy principle limit that determines the spatial resolution can applied...

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