intro

1. Intensity of Raman band and
Raman Depolarization Ratio
Ghada Bint E Sajid
M.Sc final

2. Why we use raman
spectroscopy?
• Use to determine molecular
motion especially the
vibrational one

3. What exactly is being
measured?
• When light hits a sample,it is
excited and is force to vibrate
and move.It is these vibrations
which we are measuring.

4. .
• The Raman scattered light
consists of the parallel
component and the
perpendicular component

5. Perpendicular component
• Some fraction of the Raman
scattered light has a polarization
direction that is perpendicular to
that of the incident light. This
component is called the
perpendicular component.

6. Parallel component
• The component of the Raman
scattered light whose polarization
direction is parallel to that of the
incident light is called the parallel
component

7. .
.

8. .
• Polarizibility
Ease of distortion of a bond
• Polarization
Property of beam of radiation and
describes the plane in which the radiation
vibrates

9. Depolarization ratio
Intensity ratio between the
perpendicular component and
the parallel component of the
Raman scattered light.

10. .
For completely plane polarized
light,intensity of perpendicular
component is equal to zero and
hence the degree of
depolarization is also zero.

11. .
• for completely unpolarized (i.e.
ordinary) light,intensity of parallel
and perpendicular component is
equal and depolarization ratio is
equal to 1

12. .
• Experimently,the
depolarization ratio may be
obtained by inserting a
polarizer between a sample
and the monochromator

13. Factors
• Symmetry of the molecule and
• Normal vibrational mode, in other
words, the point group of the
molecule

14. .
Depolarization ratio of a totally
symmetric vibrational mode is
less than 0.75, and that of the
other modes equals 0.75.

15. Polzaried band
• A Raman band whose
depolarization ratio is less than
0.75.vibration is totally symmetric.

16. Depolarized band
A band with a 0.75
depolarization ratio is called a
depolarized band.vibration is
not symmetric.

17. .
• The depolarization ratio can
be useful in interpreting the
actual vibration responsible
for a raman signal.

18. Intensity of raman band
• The Raman scattering intensity is mainly
affected by the:
• Light source intensity (directly proportional)
• Wavelength of the source (l-4dependency)
• Concentration of the sample or number of
molecules (directly proportional)
• Scattering properties of the sample (sample
specific)

19. Refrences
• Charly D. Allemand, "Depolarization Ratio
Measurements in Raman Spectrometry",
Applied Spectroscopy 24(3), 1970, pp. 348–353
• Jump up ^ D. A. Long (Apr 8, 1953). "Intensities
in Raman Spectra. I. A Bond Polarizability
Theory". Proceedings of the Royal Society of
London. Series A
• C N Banwell
• Wikipedia,the free encyclopedia

20. .
Thank you