Raman scattering

Raman Scattering, commonly referred as the Raman Effect, is a phenomena in which photons are scattered inelastically by matter, with the scattered photon’s frequency differing from that of the input photon. It implies that as the photon reaches the surface of the matter, the energy level and direction of the light will change. The effect occurs when incoming photons from a visible laser are shifted to lower energy, causing a molecule to gain vibrational energy. Sir C.V. Raman invented Raman scattering with the help of his pupil K.S. Krishnan. In 1930, Dr. Raman was given the Nobel Prize in Physics for finding the same. 

Raman scattering

When light collides with molecules in the air, it scatters as soon as it hits the molecule’s surface. Elastic scattering, commonly known as Rayleigh scattering, is the most common mechanism of scattering. The protons’ energy is not altered in Raman Scattering. Furthermore, there is a possibility that the incident photon interacts with the molecule in such a way that energy is acquired or lost, and the photons’ frequency shifts. The Raman Scattering is a type of inelastic scattering.

Only a limited percentage of photons can be scattered in an inelastic manner (1 in 10 million approximately). The Raman Dispersed Photons are scattered photons that have a change in their energy level (typically lower energy).

Raman The polarity of the molecule affects scattering. The incident photon stimulates the molecules’ vibrational modes, resulting in lower-energy scattered photons. Spectral satellite lines will be visible below the Rayleigh scattering peaks at the incident frequency if scattered light is examined spectrally. These are known as ‘Stokes lines.’ However, as the vibrational energy is added to the photon incidental energy, it is conceivable to detect scattering at frequencies exceeding incident frequency when there is a high level of excitation of the vibrationally excited states of the scattering molecules. These are described as ‘anti-stokes lines’ because they are often weaker.                               

Degree of Freedom

The degree of freedom, or DOF, is a set of independent characteristics that determine the physical system’s configuration. The Degree of Freedom formula is as follows:

DF=n-1

[Where DF stands for Degree of Freedom and N is for Number of Samples]

There are a total of 3N degrees of freedom for each molecule (N = number of atoms). The ability of a molecule to go in all 3 directions determines its degree of freedom. Transitional, rotational, and vibrational motions are the three types of motion that make up this 3N degree of freedom.

The translational motion of the particle along the three spatial dimensions corresponds to the three degrees of freedom. Because the position of the atoms in the molecule is not altered by the bond axis, linear molecules only have two rotations. The molecule’s vibrational modes are represented by the remaining degrees of freedom.

Raman Spectrum

The Raman spectrum is the spectrum of a dispersed photon. The dispersed photon’s wavelength is converted to a wavenumber, and the wavenumbers are shown on the x-y plane. The wavenumbers are shown on the y-axis with the Raman intensity on the x-axis. In Raman Spectrum, the difference between wavenumbers and intensity is detected. A Raman Spectrum exhibits a number of peaks that represent the scattered light’s intensity and wavelength position. Each peak in the spectrum corresponds to a unique chemical vibration that comprises both individual and group bonds.                                         

Raman Spectroscopy

Raman Spectroscopy is a non-destructive chemical analysis technique that is used to examine the chemical structure of a molecule. It is self-evident that Raman scattering is used to investigate such chemical entities. Raman Spectroscopy was invented by Sir C.V Raman to examine vibrational, rotational, and low-frequency phases.

Stimulated Raman scattering and Raman amplification

The Raman scattering process, as stated above, occurs spontaneously; that is, one of the many incoming photons is dispersed by the material at random time intervals. Spontaneous Raman scattering is the name given to this process.

Stimulated Raman scattering, on the other hand, can occur if some Stokes photons had previously been created by spontaneous Raman scattering (and somehow made to remain in the material), or when Stokes photons (“signal light”) are purposely injected alongside the original light (“pump light”). In this situation, the overall Raman scattering rate is higher than spontaneous Raman scattering because pump photons are transformed into extra Stokes photons more quickly. The higher the number of Stokes photons already existing, the faster more are added.  which is used in Raman amplifiers and Raman lasers, effectively amplifies the Stokes light in the presence of the pump light.

Applications of Raman scattering

Raman spectroscopy is employed in a wide range of applications, including non-destructive, microscopic, chemical analysis, and imaging. Raman analysis can deliver critical information fast and easily, whether the goal is qualitative or quantitative data. It can be used to quickly determine a sample’s chemical composition and structure, if it’s a solid, liquid, gas, gel, slurry, or powder.

The following explanation focuses on a few important domains where Raman is well-established and its value is well acknowledged. 

Raman spectroscopy’s most renowned applications:

Compound distribution in tablets

homogeneity of the blend

Screening with a high throughput

Concentration of API

Purity and quantity of powder

Verification of raw materials

Forms that are polymorphic.

Conclusion

Raman Scattering, commonly referred as the Raman Effect, is a phenomena in which photons are scattered inelastically by matter, with the scattered photon’s frequency differing from that of the input photon. It implies that as the photon reaches the surface of the matter, the energy level and direction of the light will change.

The degree of freedom, or DOF, is a set of independent characteristics that determine the physical system’s configuration. The Degree of Freedom formula is as follows:

DF=n-1

The Raman scattering process, as stated above, occurs spontaneously; that is, one of the many incoming photons is dispersed by the material at random time intervals. Spontaneous Raman scattering is the name given to this process.