This document provides an overview of Raman spectroscopy. It begins with an introduction, explaining that Raman spectroscopy involves measuring the wavelength and intensity of inelastically scattered light from molecules. This scattered light occurs at shifted wavelengths corresponding to molecular vibrations.
It then provides a brief history of Raman spectroscopy and its development. The document outlines some key aspects of Raman spectroscopy, including that it is a vibrational spectroscopy that is complementary to infrared spectroscopy. Raman spectroscopy can be used to study samples with minimal preparation across various physical states.
The remainder of the document discusses various technical aspects of Raman spectroscopy in more detail, including classical theories, instrumentation components like lasers and filters, and conditions required for Raman scattering to occur. It provides examples
Raman Spectroscopy - Principle, Criteria, Instrumentation and ApplicationsPrabha Nagarajan
Basic principle of Raman scattering- Difference between Rayleigh and Raman Scattering- Major criteria for Raman active in compounds,-Stroke's lines and Anti-stoke lines- Difference and between IR and Raman spectroscopy- Wide applications of Raman spectroscopy.
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Raman Spectroscopy - Principle, Criteria, Instrumentation and ApplicationsPrabha Nagarajan
Basic principle of Raman scattering- Difference between Rayleigh and Raman Scattering- Major criteria for Raman active in compounds,-Stroke's lines and Anti-stoke lines- Difference and between IR and Raman spectroscopy- Wide applications of Raman spectroscopy.
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NQR - DEFINITION - ELECTRIC FIELD GRADIENT - NUCLEAR QUADRUPOLE MOMENT - NUCLEAR QUADRUPOLE COUPLING CONSTANT - PRINCIPLE OF NQR - ENERGY OF INTERACTION - SELECTION RULE - FREQUENCY OF TRANSITION - APPLICATIONS
It contains the basic principle of Mossbauer Spectroscopy.
Recoil energy, Dopler shift.
The instrumentation of Mossbauer Spectroscopy.
Hyperfine interactions.
Nmr nuclear magnetic resonance spectroscopyJoel Cornelio
Basics of NMR. Suitable for UG and PG courses.
Includes principle, instrumentation, solvents. chemical shift and factors affecting it. Some problems. resolving agents, coupling constant and much more
A ppt compiled by Yaseen Aziz Wani pursuing M.Sc Chemistry at University of Kashmir, J&K, India and Naveed Bashir Dar, a student of electrical engg. at NIT Srinagar.
Warm regards to Munnazir Bashir also for providing us with refreshing tea while we were compiling ppt.
NQR - DEFINITION - ELECTRIC FIELD GRADIENT - NUCLEAR QUADRUPOLE MOMENT - NUCLEAR QUADRUPOLE COUPLING CONSTANT - PRINCIPLE OF NQR - ENERGY OF INTERACTION - SELECTION RULE - FREQUENCY OF TRANSITION - APPLICATIONS
It contains the basic principle of Mossbauer Spectroscopy.
Recoil energy, Dopler shift.
The instrumentation of Mossbauer Spectroscopy.
Hyperfine interactions.
Nmr nuclear magnetic resonance spectroscopyJoel Cornelio
Basics of NMR. Suitable for UG and PG courses.
Includes principle, instrumentation, solvents. chemical shift and factors affecting it. Some problems. resolving agents, coupling constant and much more
A ppt compiled by Yaseen Aziz Wani pursuing M.Sc Chemistry at University of Kashmir, J&K, India and Naveed Bashir Dar, a student of electrical engg. at NIT Srinagar.
Warm regards to Munnazir Bashir also for providing us with refreshing tea while we were compiling ppt.
Although the inelastic scattering of light was predicted by Adolf Smekal in 1923, it was not observed in practice until 1928. The Raman effect was named after one of its discoverers, the Indian scientist C. V. Raman, who observed the effect in organic liquids in 1928 together with K. S. Krishnan, and independently by Grigory Landsberg and Leonid Mandelstam in inorganic crystals. Raman won the Nobel Prize in Physics in 1930 for this discovery. The first observation of Raman spectra in gases was in 1929 by Franco Rasetti.
Raman Spectroscopy is a non destructive chemical analysis technique which provides detailed information about chemical structure, crystallinity and molecular interactions. The raman effect involves scattering of light by molecules of gases, liquids, or solids. Raman Spectroscopy is sensitive to homo-nuclear molecular bonds. It is able to distinguish between single, double, and triple bonds between carbon atoms.Raman spectroscopy is the study of matter by the inelastic scattering of monochromatic
light. It has become a ubiquitous tool in modern spectroscopy, biophysics, microscopy, geochemistry, and analytical chemistry. In contrast to typical absorption or emission spectroscopy experiments, transitions among quantum levels of atoms or molecules are induced by the absorption or emission of photons (IR, visible, UV). In a typical Raman experiment, a polarized monochromatic light source (usually a laser) is focused into a sample, and the scattered light at 90 degree
to the laser beam is collected and dispersed by a high-resolution monochromator. The incident laser wavelength (chosen such that
the sample does not absorb, in ordinary Raman Spectroscopy) is fixed, and the scattered light is
dispersed and detected to obtain the frequency spectrum of the scattered light. The scattered light is very weak
(<10-7 of the incident power), so that monochromators with excellent straylight rejection and sensitive detectors are required. In a much rarer event (approximately 1 in 10million photons)Raman scattering occurs, which is an inelastic scattering process with a transfer of energy between the molecule and scattered photon. If the molecule gains energy from the photon during the scattering (excited to a higher
vibrational level) then the scattered photon loses energy and its wavelength increases which is called Stokes Raman scattering . Inversely, if the molecule loses energy by relaxing to alower vibrational level the scattered photon gains thecorresponding energy and its wavelength decreases;
which is called Anti-Stokes Raman scattering. • Quantum mechanically Stokes and Anti-Stokes areequally likely processes. However, with an ensemble of molecules, the majority of molecules will be in the ground vibrational level (Boltzmann distribution) and Stokes scatter is the statistically more probable process. As a result, the Stokes Raman scatter is always more intense than the anti-Stokes and for this
reason, it is nearly always the Stokes Raman scatter that is measured in Raman spectroscopy. Raman spectroscopy is used in chemistry to identify molecules and study chemical bonding and intramolecular bonds.In solid-state physics, Raman spectroscopy is used to characterize materials, measure temperature, and find the crystallographic orientation of a sample . In nanotechnology, a Raman microscope can be used to analyze nanowires to better understand their structures, and the radial breathing mode of carbon nanotubes is commonly used to evaluate their diameter.
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2. INTRODUCTION
• Raman spectroscopy is the measurement of the
wavelength and intensity of inelastically scattered
light from molecules. The Raman scattered light
occurs at wavelengths that are shifted from the
incident light by the energies of molecular
vibrations.
• Raman spectroscopy is used to determine the
molecular motions, especially the vibrational
one.
2
3. Time lap
• 1923 – Inelastic light scattering is predicted by A. Smekel
• 1928 – Landsberg and Mandelstam see unexpected frequency shifts in
scattering from quartz
• 1928 – C.V. Raman and K.S. Krishnan see “feeble fluorescence” from
neat solvents
• 1930 – C.V. Raman wins Nobel Prize in Physics
• 1961 – Invention of laser makes Raman experiments reasonable
• 1977 – Surface-enhanced Raman scattering (SERS) is discovered
• 1997 – Single molecule SERS is possible
3
4. OVERVIEW
• A vibrational spectroscopy
- IR and Raman are the most common vibrational spectroscopes for
assessing molecular motion and fingerprinting species
- Based on inelastic scattering of a monochromatic excitation source
- Routine energy range: 200 - 4000 cm–1
• Complementary selection rules to IR spectroscopy
- Selection rules dictate which molecular vibrations are probed
- Some vibrational modes are both IR and Raman active
• Great for many real-world samples
- Minimal sample preparation (gas, liquid, solid)
- Compatible with wet samples and normal ambient
- Achilles Heal is sample fluorescence
4
5. Raman spectrometer’s mechanism.
When a substances (in any state) is irradiated with a monochromatic light
of definite frequency(v),the light scattered at right angle to the incident
light contains lines of 1. Incident frequency and 2.Also of lower
frequency
Sometimes lines of higher frequency are also obtained that of the incident
beam will be scattered. It is called Raman scattering.
The line with lower frequency are called Stoke’s lines.
Also, the line with higher frequency are called Antistoke’s lines.
The line with the same frequency as that of the incident light is called
Rayleigh line.
5
8. • It may be noted that raman frequencies for a
particular substances are characteristic of that
substances.
• The various observation made by raman are
called raman effect.
• Also the spectrum obtained is called raman
spectrum.
8
9. Classical theory of raman effect
• According to the classical theory of electromagnetic radiation, electric and magnetic fields
oscillating at a given frequency are able to give out electromagnetic radiation of the same
frequency. One could use electromagnetic radiation theory to explain light scattering
phenomena.
• For a majority of systems, only an induced electric dipole moment μ is taken into
consideration. This dipole moment which is induced by the electric field E could be
expressed by the power series
μ=μ(1)+μ(2)+μ(3)+⋯
where
μ(1)=α⋅E
μ(2)=12β⋅EE
μ(3)=16γ⋅EEE
α is termed the polarizability tensor.
It is a second-rank tensor with all the components in the unit of CV-1m2. Typically, orders of
magnitude for components in α, β, and γ are as follows,
α, 10-40 CV-1m2;
β, 10-50 CV-2m3; and
γ, 10-61 CV-3m4.
According to the values, the contributions of μ(2)and μ(3) are quite small unless electric field is
very high. Since Rayleigh and Raman scattering are observed quite readily with very much
lower electric field intensities, one may expect to explain Rayleigh and Raman scattering in
terms of μ(1) only.
9
10. Classical theory of raman effect
y of Raman Effect
Colthup et al., Introduction to Infrared and Raman Spectroscopy, 3rd ed., Academic Press, Boston: 1990
mind = aE
polarizability
10
11. .
Electronic
Ground State
1st Electronic
Excited State
ExcitationEnergy,s(cm–1)
Vib.
states
4,000
25,000
0
fluorescence
IR
s
s semit
2nd Electronic
Excited State
Raman
∆s=semit-s
s ∆s
fluorescence
Impurity
Fluorescence
= Trouble
Raman Spectroscopy: Absorption, Scattering, and Fluorescence
Stokes Anti-Stokes
11
12. . Raman Spectroscopy: Classical Treatment
• Number of peaks related to degrees of freedom
DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atoms
• Energy related to harmonic oscillator
• Selection rules related to symmetry
Rule of thumb: symmetric=Raman active, asymmetric=IR active
Raman: 1335 cm–1
IR: 2349 cm–1
IR: 667 cm–1
CO2
s or s
c
2
k(m1 m2)
m1m2
Raman + IR: 3657 cm–1
Raman + IR: 3756 cm–1
Raman + IR: 1594 cm–1
H2O
12
13. Theory of raman spectra
Two cases may arise depending upon whether a collision between a photon and molecules
In it’s ground state is elastic or inelastic in nature.
Case 1- if the collision is elastic – this lead to the appearance of unmodified lines (or
unmodified frequency of light) in the scattered beam and this explain rayleigh scattering.
Case 2 - if the collision is inelastic – there will be exchange or transfer of energy between
the scattering molecules and the incident photon.
The frequency of scattered light and the incident photon which is either higher or lower
than that of the incident photon is called raman frequency.
Totalenergybeforecollision=totalenergyaftercollision
13
15. Rayleigh Scattering:- Occurs when incident EM radiation induces an
oscillating dipole in a molecules, which is re-radiated at the same frequency.
Eugene Hecht, Optics, Addison-Wesley, Reading, MA, 1998.
•Elastic (l does not change)
•Random direction of emission
•Little energy loss
•of emission
•Little energy loss
4 2 2
0
4 2
8 ( ') (1 cos )
( )sc
E
E
d
a
l
15
16. Raman Scattering
Occurs when monochromatic light is scattered light has been weakly modulated
by the characteristic frequencies of the molecules.
Raman spectroscopy measures the differences between the wavelengths of the
incident radiation and the scatted radiation.
max 0
max max 0
max max 0
( ) cos2
1
cos2 ( )
2
1
cos2 ( )
2
equil
z zz
zz
vib
zz
vib
t E t
d
r E t
dr
d
r E t
dr
m a
a
a
Selection rule: v = ±1
Overtones: v = ±2, ±3, …
Must also have a change in polarizability
Classical Description does not suggest any difference
between Stokes and Anti-Stokes intensities
1
0
vibh
kT
N
e
N
16
17. The Raman polarization
The Raman Polarization is a property of waves that can oscillate with more
than one orientation EMR or waves, such as light and gravitational wave
exhibit polarization.
Polarization state :- the shape traced out in a fixed plane by the electric
vector as such a plane wave passes over it is a description of the
polarization.
E.g. linear polarization
circular polarization
elliptical polarization
orthogonally polarization
Polarization changes are necessary to form the virtual state and hence the
Raman effect.
17
18. Condition for raman spectroscopy
Vibrational modes that are more polarizable are more Raman-active
Examples:
– N2 (dinitrogen) symmetric stretch
cause no change in dipole (IR-inactive)
cause a change in the polarizability of the bond – as the bond gets
longer it is more easily deformed (Raman -active)
– CO2 asymmetric stretch
cause a change in dipole (IR-active)
Polarizability change of one C=O bond lengthening is cancelled by
the shortening of the other – no net polarizability (Raman-inactive)
Some modes may be both IR and Raman-active, others
may be one or the other!
18
19. Condition for raman spectroscopy
Raman spectra occurs as a result of oscillation of a dipole
moment, induced in a molecules by the oscillating electric field of
an incident wave.
As the induced dipole moment is directly proportional to the
polarisability of the molecules, the molecules must possess
anisotropic polarisability which should change during molecular
rotation or vibration for vibrational or rotational-vibrational raman
spectra.
Anisotropic polarisability depends upon the orientation of the
molecules.
In the presence of an electric field, the electron cloud of an atom
or molecules is distorted or polarised.
19
20. Mutual Exclusion Principle
For molecules with a center of symmetry, no IR active
transitions are Raman active and vice versa
Symmetric molecules
IR-active vibrations are not Raman-active.
Raman-active vibrations are not IR-active.
O = C = O O = C = O
Raman active Raman inactive
IR inactive IR active
20
22. There are following component
involves.
1. Laser or source of light
2. Filter
3. Sample holder
4. detector
22
23. The block design dispersive Raman scattering
system:
Radiation
sources
Sample
Wavelength
selector
Detector
InGaAs or
Ge
RecorderDetector
InGaAs or
Ge
Recorder
Detector
InGaAs or
Ge
Recorder
Block diagram
23
90·
26. 1. Laser or source of light
• Lasers are generally the only source strong enough to scatter lots of light and
lead to detectable raman scattering.
• Lasers operate using the principle of stimulated emission.
• Electronic population inversion is required to achieve gain via stimulated
emission (before the fluorescence lifetime is reached)
• Population inversion is achieved by “pumping” using lots of photons in a
variety of laser gain media
26
27. List of Various laser source
S.No. Laser wavelength
01 Nd:YAG 1064nm
02 He:Ne 633nm
03 Argon ion 488nm
04 GaAlAs diode 785nm
05 Co2 10600nm
06 Ti-Sapphire 800nm
27
28. A :- He:Ne laser
• Filled with 7:1 He & Ne gas optimum output of 6328 Å
• High voltage excitation is preferred
B :- Nd:YAG System
• A typical laser system –the neodymium-doped yttrium aluminum garnet or Nd+3
• YAG is a cubic crystalline material
• Crystal field splitting causes electronic energy level splitting
• Nd:YAG laser are optically pumped using a flash tube or laser diodes.
• These are the one of the most common type of laser.
• It emits 1064 nm wavelength
28
29. 2.Filter
• It is therefore essential to have monochromatic radiations.
• For getting monochromatic radiations filters are used.
• They may be made of nickel oxide glass or quartz glass.
• Sometimes a suitable colored solution such as an aqueous
solution of ferricyanide or iodine in CCl2 may be used as a
monochromator.
29
30. 3.Sample holder
• For the study of raman effect the type of sample holder to be used
depends upon the intensity of sources ,the nature and availability
of the sample.
• The study of raman spectra of gases requires samples holders
which are generally bigger in size than those for liquids.
• Solids are dissolved before subjecting to raman spectrograph.
• Any solvents which is suitable for the ultraviolet spectra can be
used for the study of raman spectra.
• Water is regarded as good solvents for the study of inorganic
compounds in raman spectroscopy. 30
31. 4.detector
• Researchers traditionally used single points detectors such as
photocounting, photomultiplier(PMT), not because of the weakness of a
typical raman signal, longer exposure times were often required to obtains
raman spectrum of a decent quality.
• Now days multichannel detectors like photodiode arrays(PDA), charged
couple devices(CCD)
• Sensitivity & performance of modern CCD detectors are high.
31
32. APPLICATION
Pharmaceuticals and Cosmetics:-
• Compound distribution in tablets
• Blend uniformity
• High throughput screening
• API concentration
• Powder content and purity
• Raw material verification
• Polymorphic forms
• Crystallinity
• Contaminant identification
• Combinatorial chemistry
• In vivo analysis and skin depth profiling
32
33. • Geology and Mineralogy
• Raman spectra of (top to bottom) olivine, apatite, garnet and
gypsum illustrating how Raman can be used for fast mineral ID.
• Gemstone and mineral identification
• Fluid inclusions
• Mineral and phase distribution in rock sections
• Phase transitions
• Mineral behavior under extreme conditions
33
34. Carbon Materialss
• Peak fitting of the D and G bands in a DLC spectrum
• Single walled carbon nanotubes (SWCNTs)
• Purity of carbon nanotubes (CNTs)
• Electrical properties of carbon nanotubes (CNTs)
• sp2 and sp3 structure in carbon materials
• Hard disk drives
• Diamond like carbon (DLC) coating properties
• Defect/disorder analysis in carbon materials
• Diamond quality and provenance
34
36. Life Sciences
• Multivariate clustering of spectra acquired from three bacterial
species, illustrating how Raman can be used to characterise and
distinguish bacteria at the single cell level.
• Bio-compatibility
• DNA/RNA analysis
• Drug/cell interactions
• Photodynamic therapy (PDT)
• Metabolic accretions
• Disease diagnosis
• Single cell analysis
• Cell sorting
• Characterisation of bio-molecules
• Bone structure
36
37. Differences between IR and Raman methods
S.No Raman IR
01 It is due to the scattering of light
by the vibrating molecules.
It is the result of absorption of
light by vibrating molecules.
02 The vibration is Raman active if it
causes a change in polarisability.
Vibration is IR active if there is
change in dipole moment.
03 The molecule need not possess a
permanent dipole moment.
The vibration concerned should have a
change in dipole moment due to that
vibration.
04 Water can be used as a solvent. Water cannot be used due to its
intense absorption of IR.
05 Sample preparation is not very
elaborate, it can be in any state.
Sample preparation is elaborate
Gaseous samples can rarely be
used.
06 Gives an indication of covalent
character in the molecule.
Gives an indication of ionic
character in the molecule.
07 Cost of instrumentation is very
high
Comparatively inexpensive.
37
38. Advantages of Raman over IR
• Water can be used as solvent.
• Very suitable for biological samples in native state (because water
can be used as solvent).
• Although Raman spectra result from molecular vibrations at IR
• frequencies, spectrum is obtained using visible light or NIR
• radiation.
• =>Glass and quartz lenses, cells, and optical fibers can be used.
• Standard detectors can be used.
• Few intense overtones and combination bands => few spectral
overlaps.
• Totally symmetric vibrations are observable.
• Raman intensities a to concentration and laser power.
38
39. Advantages of IR over Raman
• Simpler and cheaper instrumentation.
• Less instrument dependent than Raman spectra because IR spectra
are based on measurement of intensity ratio.
• Lower detection limit than (normal) Raman.
• Background fluorescence can overwhelm Raman.
• More suitable for vibrations of bonds with very low polarizability
(e.g. C–F).
39
40. Several variations of Raman
spectroscopy
1. Surface-enhanced Raman spectroscopy (SERS) – Normally
done in a silver or gold colloid or a substrate containing silver or
gold. Surface plasmons of silver and gold are excited by the laser,
resulting in an increase in the electric fields surrounding the metal.
• Given that Raman intensities are proportional to the electric field,
there is large increase in the measured signal (by up to 1011).
• This effect was originally observed by Martin Fleischmann but the
prevailing explanation was proposed by Van Duyne in 1977.
• A comprehensive theory of the effect was given by Lombardi and
Birke.
40
41. 2. Resonance Raman spectroscopy
The excitation wavelength is matched to an
electronic transition of the molecule or crystal, so
that vibrational modes associated with the excited
electronic state are greatly enhanced. This is useful
for studying large molecules such as polypeptides,
which might show hundreds of bands in
"conventional" Raman spectra. It is also useful for
associating normal modes with their observed
frequency shifts.
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42. 3. Surface-enhanced resonance Raman
spectroscopy (SERRS) – A combination of SERS
and resonance Raman spectroscopy that uses proximity to
a surface to increase Raman intensity, and excitation
wavelength matched to the maximum absorbance of the
molecule being analysed.
4. Coherent anti-Stokes Raman
spectroscopy (CARS) –
Two laser beams are used to generate a coherent anti-Stokes
frequency beam, which can be enhanced by resonance.
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43. 5. Raman optical activity (ROA) – Measures
vibrational optical activity by means of a small difference in the
intensity of Raman scattering from chiral molecules in right-
and left-circularly polarized incident light or, equivalently, a
small circularly polarized component in the scattered light.
6. Spatially offset Raman spectroscopy (SORS)
7. Spontaneous Raman spectroscopy (SRS)
8. Optical tweezers Raman spectroscopy (OTRS)
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