Raman spectra

RAMAN EFFECT

1. 1 KAMLA NEHRU INSTITUTE OF PHYSICAL & SOCIAL SCIENCE SULTANPUR(U.P.) DEPARTMENT OF physics SEMINOR TOPIC RAMAN EFFECT SESSION: 2016 -17 Submitted to: Dr . S.K. SRIVASTAVA H.O.D PHYSICS KNIPSS SULTANPUR Submitted By : VIVEK VISHWAKARMA M.Sc. PRE. PHYSICS KNIPSS SULTANPUR UNDER SUPERVISION Mr. RAHUL YADAV

2. RAMAN SPECTRA Introduction :- Rayleigh observed that if a substance is irradiated with mono chromatic Light, the scattered light is observed in a direction at right angles to the incident light. This is shown in fig.4.1

3. When a spectroscope was used to investigate the scattered Light, it was found that the frequency of Scattered Light was same as the frequency of the incident raditions. This phenomenon was observed By rayleigh and is known as was observed by rayleigh and known as Rayleigh Scattering. In 1923 Smekel predicted theoretically that if a S ubstance in the gaseous, liquid or solid state in irradiated with monochromatic light, the scattered light should contain radiations with different frequencies than the frequency of incident light. Raman Effect :- In 1928 Sir C.V. Raman discovered that when a beam of monochromatic light was allowed to pass through a substance in the solid, liquid or gaseous state, the scattered Light contains some additional frequencies over and over that of incident frequency. This is Known as Raman Effect . and is a beautiful confirmation of the smekels prediction.

4. The lines whose wave lengths have been modified in Rama effect are called Raman lines. The lines having wave lengths greater than that of incident wavelengths are stokes lines and those having shorter wave lengths anti stokes lines and those having shorter wave lengths Anti- stokes lines if V i is frequency of incident radiation and V s is the radiation scattered by the giving Molecule species, then the Raman shift ∆V= V i – V s. The Raman shift does not depend upon the frequency of incident light but it is regarded as a characteristic of the Substance causing Raman effect. For stokes line, ∆V is positive and for anti stokes lines ∆V is negative.(Fig.-4.2&4.3)

5. Characteristic properties of Raman lines :- The lines Observed in Raman effect exhibit a number of characteristic which are Summarished as follows : The intensity of stocks lines is always greater than the corresponding anti stokes lines. Raman shift ∆V generally lines within far and near infrared regions of the spectrum It means that the Raman frequencies are generally identical with the infrared vibrational Frequencies. (The small difference can be attributed to experimental errors) it should be noted that it is not necessary that all Raman lines will have their corresponding infrared bands are similarly all infrared band’s may not have the corresponding Raman Lines. 3. Raman Lines are symmetrically displaced about the parent lines when the temperature rises, their individual separations from the parent lines decrease.

6. 4. The frequency difference between the modified and parent lines represent the frequency of the absorption band of the material. Physical Significance :- Since the Raman effect depends upon the polarizability of the molecule it can be observed For molecules which have no net dipole moment and therefore produce no pure rotational spectrum this process can yield information about the moment of intra and hence the structure of molecule. In Roman effect an intense monochromatic light source give scattered light which includes one or more “side bonds” that are offset by rational and/or irrational energy difference .This is potentially very useful for remote sensing. Since the sideband frequencies contain information about the scattering medium which could be useful for identification .

7. In Raman effect water can be used as a solvent while in I.R. spectroscopy water can not be used as a solvent because it is opaque to infrared radiation. Application of Raman Spectra : The Raman effect is very important because of its large number of applications. In fact it is an useful tool for solving the intricate research problems concerning .The constitution of compounds. The application of Raman effect are very much and ever increasing and therefore, it is not possible to include all the applications. Some of its application are discussed below. 1. All substances to be analyzed by Raman spectroscopy should be free from impurities Likely To absorb in the range of Raman spectrum. Gas chromatography or Vacuum distillation Can be used for purification of liquids. Crystalline substances can be examined in solution as a melt in powered form or as single crystals. Solvent are purified by distillation in grease free apparatus or by filtration through alumina .