How does raman spectroscopy work

Raman scattering is a weak phenomena and fluorescence can swamp the signal making it difficult to collect quality data. This issue often can be alleviated by using a longer wavelength excitation source. With respect to reaction analysis, Raman spectroscopy is sensitive to many functional groups but is exceptional when obtaining molecular backbone information, providing its own unique molecular fingerprint.

Because Raman utilizes a bonds polarizability and has the potential to measure lower frequency, it is sensitive to crystal lattice vibrations giving the user polymorphic information that can be challenging to obtain by FTIR. This allows Raman to be used very effectively to study crystallization and other complex processes.

A modern, compact Raman spectrometer consists of several basic components, including a laser that serves as the excitation source to induce the Raman scattering. Typically, solid state lasers are used in modern Raman instruments with popular wavelengths of nm, nm, nm and nm. 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.

For this reason, many Raman systems feature the nm laser. The laser energy is transmitted to and collected from the sample by fiber optics cables. 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.

A CCD detector captures the light, resulting in the Raman spectrum. Since Raman scattering yields a weak signal, it is most important that high-quality, optically well-matched components are used in the Raman spectrometer.

When spectrum is collected consistently over the course of an experiment, it can reveal a 'molecular video' that provides key information regarding the kinetics, mechanisms, and form changes during a reaction. Traditionally, this analysis has been performed by spectroscopists with expert knowledge in finding key areas of interest and trending these wavenumbers over time.

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. Compact Performance. ReactRaman combines best in class performance with a flexible design.

The spectrometer is small, light, and thermally stable, delivering outstanding results wherever it's needed. Fast, Accurate Results. Integrated Platform. Shared Expertise. With over 30 years of reaction analysis expertise, we are committed to developing high-performance solutions so that scientists can solve challenging chemistry problems.

Dow Toray Co. For a wide range of industries, silicone's diverse properties enable companies to design products with specific, fit-for-purpose characteristics. These products exploit the varied properties of silicone rubbers such as strength, thermal resistivity and stability.

Typically, silicone is produced via hydrolysis of a chlorosilane followed with a terminal functional group addition, or through polycondensation of a cyclic siloxane. Each of these methods are equilibrium reactions that produce low-molecular-weight products with a wide range molecular weight distribution. Dow researchers have developed an alternate means of producing silicone, based on a precisely controlled polymerization, to yield product with targeted, uniform chain lengths.

In this synthesis, a lithium-based reactant serves to open a cyclic tri-siloxane ring, followed by addition of another cyclic siloxane reagent, to yield a monodispersed silicone polymer. This novel silicone polymerization, which results in monodispersed product with precisely controlled chain lengths, is tracked by ReactRaman , eliminating the delays and reaction uncertainties associated with offline GC analysis.

Reaction initiation, progress and kinetics are all readily measured by the Raman method , providing continuous, real time verification that the reaction is proceeding as expected.

Designed specifically for chemical and process development, these tools are combined across the powerful iC software platform to provide comprehensive process understanding.

This free online event on October 27, is for those interested in learning new methods to design, monitor and control flow processes using Raman spectroscopy. Automated Reactors and In Situ Analysis. For Raman spectroscopy, visible light or infrared IR light is used for the excitation. The most important physical parameters and their corresponding equations relevant for Raman spectroscopy are summarized in Table 1.

When a light beam hits matter, it will interact with it in a specific way, dependent on the interplay between the light waves and the atoms and molecules that make up the matter. The interaction may leave the energy of matter and light unchanged e. The processes used in spectroscopy to characterize matter belong to the latter category.

The transfer of energy from light to matter leads to an excitation. The following section outlines the most important excitation processes required to understand Raman spectroscopy: absorption, fluorescence, and scattering.

Light energy in some parts of the electromagnetic spectrum is partially transferred to the matter. This means some light waves pass through the matter without modification transmission , while some light is absorbed by the sample. Absorption : Some of the incident wavelengths are partially absorbed in the sample, while other wavelengths are transmitted without much loss in intensity. Figure 3. Matter can reemit absorbed light again by an independent process called fluorescence.

Figure 4. When an intense light source e. However, a tiny fraction of the scattered light interacts with the matter it hits in a way that it exchanges small amounts of energy, which is called inelastic scattering. The change in energy of the scattered light results in a changed frequency and wavelength. The microscopic origin of this Raman interaction is an excitation or de-excitation of molecular vibrations in the matter.

The characteristics of these vibrations determine the wavelength of the inelastically scattered light. From measuring the intensity distribution spectrum of the scattered light it is hence possible to deduce information about the vibrational structure of the substance illuminated. Therefore, Raman spectroscopy belongs to the group of vibrational spectroscopies.

Raman scattering : Most of the incident yellow light is scattered elastically in all directions. Small amounts of light, usually with higher wavelengths orange, red , are also scattered inelastically after interaction with the molecules of the sample. Figure 5. Each of these processes can be exploited to extract information about the chemical and physical nature of the sample.

The exact type and extent of molecular properties deducible depends on the type of spectroscopy used. The two main vibrational spectroscopies are infrared IR spectroscopy and Raman spectroscopy. Raman spectroscopy employs the Raman effect for the analysis of substances. The basics of Raman scattering are explained below. There are three scattering processes that are important for Raman spectroscopy and Raman imaging techniques: [3].

Anti-Stokes Raman scattering is another inelastic scattering process. Here, a specific amount of energy is transferred from a molecular vibration to the photon. The scattered photon has higher energy and a lower wavelength than the incident photon. This process is even less likely to occur than Stokes scattering. Therefore, it is usually not used in Raman spectroscopy. The information extracted from anti-Stokes scattered light is mostly equivalent to the information extracted from Stokes scattered light, and only very specialized applications will require the extra effort to measure both scattering processes.

S tokes Raman scattering is the inelastic scattering process that transfers energy from the light to a vibration of the molecule. Therefore, the scattered photon has lower energy and a higher wavelength than the incident photon. The amount of energy transferred is not arbitrary, it has to be exactly the amount required to excite one of the molecular vibrations of the molecule.

The composition of the scattered light is therefore highly dependent on the exact type of molecule like a fingerprint. Stokes scattering is the most commonly exploited process to acquire a Raman spectrum.

It is, however, several orders of magnitude less likely to occur compared to Rayleigh scattering, rendering it difficult to detect. Rayleigh scattering is the term used for elastic scattering of light by molecules, and is by far the most dominant scattering process.

The interaction does not change the energy state of the molecule and as such the scattered photon has the same color wavelength as the incident photon. In a Raman spectrometer, the Rayleigh scattered light has to be removed from the collected light, otherwise it would obscure the Raman signals.

All vibrational spectroscopies characterize molecular vibrations and to a smaller extent also molecular rotations. Molecular vibrations are based on the movements of the individual atoms of the molecule relative to each other.

The forces keeping the molecule together will act like small springs connecting the atoms as illustrated in figure 6. The set of vibrations is highly dependent on the exact structure of the molecule and therefore comprise a unique vibrational spectrum. This makes vibrational spectroscopy an ideal tool for substance identification. Different vibrational spectroscopies can detect a different subset of the full vibrational spectrum, which is why the most common methods in this class, Raman and FT- IR, are often referred to as "complementary methods".

Raman spectroscopy detects changes in the polarizability of a molecule. It therefore only detects vibrations where the polarizability changes during the movement these are Raman-active vibrations. Figure 7: The symmetric stretching vibration of carbon dioxide CO2 increases the size of the electron cloud.

It is therefore Raman-active. But, as seen above, similar compounds will have some vibrational modes in common so they will likely share some similar peaks. The intensity of the peaks is directly proportional to the number of molecules that create the band. It is especially useful for characterizing inorganic compounds, aqueous solutions, or samples that you do not want to damage. A notable example of a sample that can only be reasonably be characterized with Raman is oil paintings.

Most oil paints, such as those used in the renaissance era, were made by combining organic oil with ground up inorganic and organic pigments. If an important painting, such as the Mona Lisa were to be restored the exact pigment mixture would be needed in order to match the original color.

With Raman spectroscopy, paints can be analyzed without damaging priceless works of art.