�ݺ�ߣ

WHAT SCATTERING IS ?
Wordly meaning
 distributing, dispersing, or separating.
In Physics
 the process in which a wave or beam of
particles is diffused or
deflected by collisions with particles of the
medium that it traverses.

HISTORY OF RAYLEIGH SCATTERING
 Rayleigh scattering named
after the British physicist Lord Rayleigh
 Discovered argon, an achievement
for which he earned the Nobel Prize
for Physics in 1904.
 He also discovered the
phenomenon now called
Rayleigh scattering,
which can be used to explain why the sky is bluE.

EXPLANATION ;
 Rayleigh scattering ( also known as preferential
scattering) is the elastic scattering of light from
particles less than approximately one-tenth the
wavelength of the light.
 The intensity of the scattered is inversely
proportional to the fourth power of the
wavelength of light ;

CONTINUE ;
 When monochromatic light is passed through a
sample, it is scattered by at an angle of 90 i.e (
perpendicular to the direction of the incident
light).
 He also found that the frequency of the incident
and scattered light is same.

 When the particle dimension are small and the
refractive index of the particle does not greatly vary
from that of the medium, the particle can behave as a
radiating dipole.
 As the wave passes the particle, the strength of the
electromegnatic field at the particle varies at the
frequency of incident radiation.
CONTINUE ;

CONTINUE ;
 If the particle can be polarized by the field a dipole is
induced that oscillates at the same frequency.
 The oscillating dipole act as a point source which
emits radiations in all directions.
 The emitted radiation from the particles has the same
wavelength as that of the incident radiation.
 Scattering that occurs by this mechanism.

CONTINUE ;
 The dipole moment µ that is induced by the electric
field of the passing electromagnetic radiation is
proportional to the electric field strength E and to the
polarizability a of the particle:
µ= aE
 The intensity of the scattered radiation is proportional
to the square of the induced dipole moment and to the
fourth power of the scattered frequency:
I= 16π⁴V⁴µ
3c³

CONCLUSION
 Normally the molecule or polyatomic ion is initially in
the lowest vibrational level of the ground electron
state.
 The energy from each photon of the incident radiation
is insufficient to cause excitation to a higher electron
level as during absorption of ultraviolet-visible
radiation.
 The scattered radiation is emitted as the particle
returns to its original energetic state.

WHY SKY IS BLUE ?
Sunlight reaches
Earth's atmosphere
and is scattered in all
directions by all the
gases and particles in
the air. Blue light is
scattered in all
directions by the tiny
molecules of air in
Earth's atmosphere.
Blue is scattered more
than other colors
because it travels as
shorter, smaller waves.

HISTORY OF RAMAN SCATTERING
Raman scattering or the Raman effect is
the inelastic scattering of a photon.
 It was discovered by C. V. Raman and K. S.
Krishnan in liquids, and by G. Landsberg and L. I.
Mandelstam in crystals. The effect had been
predicted theoretically by Adolf Smekal in 1923.

EXPLANATION
Raman scattering occurs when monochromatic light is
scattered by a molecule.Scattered radiation that has
frequency other then that of the incident radiation can
be caused by either of two mechanisms.
 Anti Stokes:
Scattering can occur only when species return to a
vibration level that is energetically lower then the initial
level. Resulting, Anti stoke has higher then that of the
incident radiation frequency.
 Stokes scattering:
Raman scattering in which the scattered radiation is
less energetic than the incident radiation a Stokes
scattering.

RAMAN ,STROKE ,ANTISTOKE LINES
 RAMAN LINES
The spectrum in which the frequency and wavelength is
being modified
 STOKELINES
Wavelength of the scattered light is more than the
wavelength of the incident light are called stoke lines
ʎs > ʎi
or
ʋs < ʋi

 ANTISTOKE LINES
Raman lines, where the wave lengths of the scattered
light is less than that of the incident light are called
antistoke lines.
ʎs < ʎi
or
ʋs >ʋi

RAMAN SHIFT
 The total change in the frequency of the incident
and scattered light (∆v) is called raman shift. It is
characteristic of each substance and depend upon
the nature of the substance.
 However raman shift doesnot depend upon the
frequency of incident light.
simply ∆v =ʋi - ʋs
∆ʋ is the raman shift
It is positive for stoke line and negative for antistoke

 Relaxation to a higher vibrational level after excitation
is more probable than relaxation to a lower level, and
Stokes scattering occurs more often than anti-Stokes
scattering.
 Stokes scattering is more often used for analysis.

DISTINCTION FROM FLUORESCENCE
 the major difference is that the Raman effect can
take place for any frequency of incident light.
 In contrast to the fluorescence effect, the Raman
effect is therefore not a resonant effect.
 this means that a fluorescence peak is anchored at
a specific frequency, whereas a Raman peak
maintains a constant separation from the excitation
frequency.

DIFFERENCE ;
RAMAN
SPECTROSCOPY
1. It involves scattering of
light.
2. Requires polarizability.
3. Sample is analyzed in
only one exposure.
4. Water canbe used as
solvent.
5. Sample cell are made of
glass.
INFRARED
SPECTROSCOPY
1. it involves the absorption
of light.
2. requires permanent
dipoles.
3. Several spectra are taken
for the sample analysis.
4. Nacl , KBr , etc made
sample cells are used.

�ݺ�ߣ

mechansim of raman scaterring

More Related Content

mechansim of raman scaterring

Editor's Notes