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ASSP Presentation.pptx

  1. Raman Effect In Solids Submitted By Muhammad Umar Farooq BSF1800603 Bilawal Hussain BSF1800308 Submitted To Dr. Muhammad Saeed Akhtar
  2. Raman Effect Raman effect, change in the wavelength of light that occurs when a light beam is deflected by molecules. When a beam of light traverses a dust-free, transparent sample of a chemical compound, a small fraction of the light emerges in directions other than that of the incident (incoming) beam.
  3. Principle When light interacts with molecules of solid, the vast majority of the photons are dispersed or scattered at the same energy as the incident photons. This is described as elastic scattering, or Rayleigh scattering.
  4. Carbon Tetrachloride CCl4 is a tetrahedral molecule with three pronounced Raman active vibrational modes. In the center of the spectrum is the Rayleigh scatter peak at the laser wavelength. 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.
  5. Raman Spectrum of electron: Inelastic scattering means that the energy of the emitted photon is of either lower or higher energy than the incident photon. After the scattering event, the sample is in a different rotational or vibrational state. This excitation puts the molecule into a virtual energy state for a short time before the photon is emitted.
  6. Raman Spectrum: •Only those rotational transitions are allowed for which ∆j=0 or ∆j= ±2 • When ∆j=0 scattered raman radiations will be same frequency • When ∆j= +2 gives stokes lines and ∆j= -2 gives anti- stokes lines
  7. Applications • Raman spectroscopy is used to identify molecules and study chemical bonding and intramolecular bonds. • Raman spectroscopy is used to characterize materials and find the crystallographic orientation of a sample. • Detection of molecular impurities and additives. • Determine molecular composition of surfaces.
  8. Characteristics of Raman Spectrum: • Intensity of stokes line is always greater than anti- stoke line • Raman shift generally lies within the far and near infrared regions • Raman lines are symmetrically displaced about rayleigh line • Raman lines are due to change in polarization of the molecules
  9. Significance: As per this concept when light travels through a fluid then there is an interaction between light and fluid which is called dispersion of light. Raman effect helps in explaining various natural phenomenon on. like appearance of blue sky, advanced sunrise and delayed sunset, etc. It also explains the appearance of red sky during sunrise and sunset.