Raman spectroscopy involves using a laser light source to illuminate a sample and analyze the scattered light. The key components are the light source, optics to direct the light, filters and monochromators to select wavelengths, and detectors to measure the scattered light. Lasers are commonly used as the light source due to their narrow linewidth and high intensity. Filters are used to remove unwanted wavelengths and isolate specific excitation lines. Monochromators are used to select narrow wavelength ranges, while detectors such as photomultiplier tubes, CCDs, and photographic plates convert the scattered light into electrical signals. Raman spectroscopy is useful for structure elucidation, quantitative analysis, studying complex formation, and applications in nanotechnology.

1. INSTRUMENTATION
Source Optics
Filters Monochromator Detector
Following are the components of raman spectrometer

3. Source of light
• Iin
In early days, Xenon and
argon lamps were used as a
source of light.
Now-a-days lasers are being
used to provide the source of
high intensity.
Advantages
• Narrow line width
• Lots of photons

4. Optics
Include mirrors
and lenses
Forms an image by
gathering rays from
an object and then
causes them to
converge or diverge

5. Filters
• Can serve as an effective
means of selectively blocking
or transmitting light based on
certain properties, such as
wavelengths or intensity.
• Similar to Monochromator,
which rely on prism dispersion
or diffraction to separate light
transmissions in order to select
a specific band of light.
Functions of filters
• To remove high energy radiation
that might cause
photodecomposition.
• To isolate a single exciting line

6. Monochromator
• Used to isolate and select a narrow range of wavelengths or
frequencies from a broader spectrum of light or
electromagnetic radiation.
• In some cases, grating is used as dispersing element.
• Not used in case of lasers.

7. Detector
• The purpose of a detector is to convert a physical signal (such as light,
radiation, or particles) into a measurable form (such as electrical signals)
for analysis or recording.
Photographic plates: It is a
glass or plastic plate coated
with a light-sensitive
emulsion, typically composed
of silver halide crystals.
Photomultiplier tube: It is a
highly sensitive detector used
to convert light or photon
signals into electrical signals.
CCD: Stands for Charge-
Coupled Device.
Have high sensitivity,
resolution and low noise.

8. Sampling in raman spectroscopy
• Sample, in the form of liquid is taken in sample tube.
• Quantity of sample is larger.
• Use of lasers reduce the need of large quantity of
sample.
• Water being raman inactive is used as solvent.

9. Interpretation of raman spectrum
• What does need to be noticed in a raman spectrum?
Raman shift
Peak
positions
Peak
intensity
Peak shape

10. Raman spectra are typically plotted as a graph
of intensity versus wavenumber.
Raman peaks in a spectrum represent the
specific vibrational modes of the molecules
present in the sample. Each peak corresponds to
a different molecular vibration.
The position (wavenumber) of a peak provides
information about the energy associated with
that vibrational mode.
Presence of different functional groups or
chemical environments within a molecule can
give rise to specific Raman peaks.
Raman
spectra
and
peaks

11. What are vibrational modes?
Vibrational
modes refer to
the different
ways in which
molecules can
vibrate
internally.

12. Correlation table

13. Raman spectra of water

14. FTIR-Raman spectrum of CO2
Red line = IR spectrum
Black line = Raman
spectrum
2349 cm-1 = Asymmetric
stretching
667 cm-1 = Bending
1330 cm-1 = Symmetrical
stretching

15. Applications of raman spectroscopy

16. 1- Structure elucidation
Series of peaks corresponds to
the different vibrational modes
Positions, intensities, and shapes
of the Raman peaks provide
valuable information about the
chemical bonds
Identify and characterize
molecules, contributing to our
understanding of their structure
and composition.
Organic
compound

17. 2-Complex formation
When molecules form a complex, the interaction between them
can result in changes to their molecular vibrations that lead to:
• Shifts in Raman peaks
• Changes in peak intensities
• Appearance of new peaks
• Peak broadening or splitting
• Intensity ratios

18. 3- Quantitative analysis
• With liquid samples, it allows to quantitative analysis with minimal
sample preparation.
• Quantitative analysis can be performed on solutions of high
concentration without the need for dilution.

19. 4- Nanotechnology

20. Why raman
spectroscopy
is not widely
used ?