Raman Spectroscopy: Principle, Instrumentation and Applications

What is Raman Spectroscopy?

Raman spectroscopy was given by an Indian Physicist Sir C.V Raman, which is based on inelastic scattering of monochromatic light with the sample. The resulting light will have a different frequency than incident light due to this inelastic scattering. 

This technique is widely used to analyze vibrational, rotational, and other low-frequency interactions in the molecule. This significantly helps in the elucidation of molecular structure, identifying functional groups, etc.

Principle of Raman Spectroscopy

Raman spectroscopy is based on the inelastic scattering of electromagnetic radiation with the molecule. We have two types of scattering that are elastic and inelastic scattering. 

Elastic scattering obeys the Rayleigh law that states that there will be no loss of energy and momentum of the incidence radiation and scattered radiation. That's why this scattering is also known as Rayleigh scattering.

Whereas, there will be some conditions (1 in million) when the energy of the scattered radiation is different from the energy of incidence radiation. This will be called inelastic scattering. These only two possibilities arise.

Raman Scattering

1. Energy of scattered radiation is less than the incidence radiation: In this type of inelastic scattering. The incidence radiation gives some of its energy to the molecule thus the scattered radiation will have less energy. This is also called Stokes Raman scattering.

2. Energy of scattered radiation is more than the incidence of radiation: In this type of inelastic scattering. The incidence radiation takes some of the vibrational/rotational energy from the molecule itself and thus the scattered radiation will have more energy. This is also called Anti-stokes Raman scattering.

Instrumentation of Raman Spectroscopy

Instrumentation of Raman spectroscopy

1. Excitation source (laser)

Raman spectroscopy uses a laser as a light source. The radiation of the spectrum depends upon the bandwidth of the laser source used. Generally, a shorter wavelength gives stronger Raman scattering.

2. Sample

A sample is placed in the sample chamber that accepts the laser and it undergoes scattering, both elastic and inelastic which further passes through the filter.

3. Filter

A filter is used in Raman spectroscopy to separate the Raman scattered light from the rayleigh scattered light. This is done to get high-quality Raman spectra. Some filters are notch, long pass, and volume halogen filters.

4. Detector

Detector helps to detect the scattered light signal. Generally, LCD array detectors are used in modern Raman spectrometers. They are optimized to detect signals of different wavelengths and even detect very weak signals.

5. Computer

A computer having suitable compatible software helps to draw a final Raman spectroscopy graph/ spectrum.

Application of Raman Spectroscopy

  1. It is used to study the structure of CO₂, N₂O, mercurous salts, chloro complexes of mercury, and the nature of bonding.
  2. It help to study physical chemistry concerning electrolytic dissociation, hydrolysis, and transition from crystalline to amorphous state.
  3. It is also used to obtain information regarding the presence or absence of specific linkages in a molecule, the structure of simple compounds, and the study of isomers.
  4. It is used for the characterization of polymer compounds by revealing the physical properties like polymer crystallinity, tacticity, amorphous character, etc.
  5. It can be easily used for rapid, easy, and accurate analysis of mixtures that are difficult with any other method.

Popular Posts

Conducting Polymers: Definition, Examples, Properties and Applications

Image
What are Conducting Polymers? As the name suggests organic polymers that conduct electricity are known as conducting polymers. They are also known as intrinsically conducting polymers (ICPs) and they have alternating single and double bonds along the polymer backbone (conjugated bonds) or that are composed of aromatic rings such as Phenylene, naphthalene, anthracene, pyrrole, and thiophene which are connected through carbon-carbon single bonds. Examples: Polyacetylene, Polypyrrole, Polyaniline, etc What is the reason behind conducting nature of these polymers? Conducting polymers comes in two forms that are doped conducting polymers and non-doped conducting polymers. The conductivity of non-doped conjugated polymers is due to the existence of a conductivity band similar to a metal. In a conjugated polymer, three of the four valence electrons form strong sigma bonds through sp² hybridization where electrons are strongly localized. The remaining unpaired electron of each carbon atom re
Read more

Crime Scene: Definition, Types and Characteristics

Image
What is a Crime Scene ? A place where the crime is committed or where the maximum physical evidence related to crime is found is known as a crime scene. A crime scene is a starting point of the investigation which provides information about the suspect and the victim. This helps to reconstruct the crime and fast resolution of the case. It is noted that the crime scene is not limited to a single place but may extend to a wider area depending upon the nature of the crime committed. For example, In a murder case where murder is done at one place and the body is disposed on another place. In this case, we have two crime scenes that give information about the crime. Types of Crime Scene Based on evidence found on the crime scene: 1. Primary Crime Scene The crime scene where the actual crime occurred or where more usable pieces of evidence were found is known as the primary crime scene. For example, A murder scene, theft, assault, etc. 2. Secondary Crime Scene The crime scene which is some
Read more

Documentation of the Crime Scene: Step by Step

Image
What is documentation of the crime scene and Why it is done? After securing the crime scene, the next most important step is documentation of the crime scene because documentation permanently records the crime scene and its physical evidence. Documentation should be done without any wastage of time as the scene and its evidence may get altered over time. The documentation should be done innovatively and the originality of the crime scene should be maintained and documentation should not have pauses or breaks, it should remain constant till the whole crime scene is documented. There are four main tasks of documentation that is note-making, photography, videography , and sketching . It should be noted that all four tasks are necessary and none is a substitute for another. For example, notes are not substitutes for photography, video is not a substitute for sketching, etc. Following are the sequence for crime scene documentation: 1. Note making Documentation of crime scene in the f
Read more