2. IR Light
• It is a kind of electromagnetic radiation
which has wavelength region longer than
visible light but shorter than radio waves.
• Moreover IR radiation carries low energy.
3. INFRARED REGIONS
• INFRARED REGIONS RANGE
• Near infrared region 0.8-2.5 μ(12,500-
4000 cm-1)
• Main infrared region 2.5-15 μ(4000-
667cm-1)
• Far infrared region 15-200 mμ(667-100
cm-1)
4. IR SPECTROSCOPY
• It is the spectroscopy that deals with the
region of electromagnetic spectrum, i.e.
the light with a longer wavelength and
lower frequency than visible light.
• Infrared Spectroscopy is the analysis of
infrared light interacting with a molecule.
• It is based on absorption spectroscopy
5. Principle of IR
• When some molecules absorb IR , it gets
excited from lower vibrational level to
higher vibrational level. ( that’s why IR
spectra is also called as Vibrational-
rotational spectra)
• All bonds are not capable of absorbing IR,
only those which are accompanied by
change in dipole moment, will absorb in IR
region(Infra red active transitions).
8. What kind of sample absorb in IR?
Only vibration which alters molecule dipole moment
(the magnitude of positive and negative charge
between two bonded atoms) and having the IR
absorption frequency in the IR region
Gas molecules such as O2, H2 and Cl2 don’t have a
dipole moment, means no IR absorption occurs
SO2 and CO2 have a dipole moment so it will give
IR absorption
9. Every functional group has their own IR absorption
The more complex in molecule structure, the more
complex in IR absorption
It is used to identify any functional group presents in a
molecule structure
10. Working of IR
IR light is passed through the sample, and the amount of energy which
is absorbed by the sample per cm wavelength will be recorded .
The IR light desired will be selected by monochromator before exposed
to the sample.
The data will be translated into the graph which is plotted as wavelength
vs transmision
The graph might be compared to known standard reference
12. IR Components
A. IR Light Sources
– Quartz halogen
– Nernst Glower lamp (run at 2000oC)
– Globar (made from Carbide silicon, run at
1100oC)
13. Sample
1. solids
– A. Nujol mull
The sample is ground using a mortar and pestle to
give a very fine powder
A small amount is then mixed with nujol (liquid
paraffin) to give a paste
Several drops of this paste are then applied
between two sodium chloride plates (these do not
absorb infrared in the region of interest)
The plates are then place in the instrument sample
holder ready for scanning
14. B. Potassium Bromide disc
– A very small amount of the solid (approximately 1-2
mg) is added to pure potassium bromide powder
(approximately 200 mg) and ground up to fine
powder.
– This is then placed in a small disc and put under
pressure mechanically. The pressure is maintained
for several minutes before removing the disc and the
KBr disc formed
– The disc is then placed in a sample holder ready
scanning
16. 2. Thin films
– The infrared spectrum of thin film can be easily
obtained by placing a sample in a suitable holder,
such as a card with a slot cut for the sample window
3. Liquids
– This is possibly the simplest and the common method
for sample preparation
– A drop of the sample is placed between two
potassium bromide or sodium chloride circular plates
to produce a thin capillary film
– The plates are then placed in a holder ready for
analysis
17.
18. 4. Gases
• For gaseous samples,it requires the use
of a cylindrical gas cell with windows at
each end composed of an infrared
inactive material such as KBr, NaCl or
CaF2
• The cell usually has an inlet and outlet
port with a tap to enable the cell to be
easilly filled with the gas to be analyzed
19. Instrumentation
Monochromator
• It break downs the radiation of light to the
selected wave region in one time running
process.
• Prism or grating type monochromators are
employed.
• Crystalline NaCl is used as prism material
20. Detectors
Thermal Detectors-
• Thermocouple is most widely used in IR
• Thermister and Bolometer
• Golay Cell
Photon Detectors-
• Made up of semiconducting material like
lead sulfide, indium antimonide,
germanium doped with Cu or Hg.
21. Display
–Exhibit the collected data
–Translate the data to the graph
–The graph is plotted as transmision vs
frequency (wavenumbers)
22. Fingerprint region (<1500 cm-1)
Many bands & many overlaps
– Heavy atom stretches
– All bends, etc.
– Should have simple molecule (or other
evidence or structure) before intepreting
bands in this region
Overall pattern reflects molecular structure
– Pattern from 1400cm- to 600cm- are known as
molecular fingerprints
23. Applications
Qualitative Analysis
• Identification of substances
• Determination of molecular structure
• Studying progress of reactions
• Detection of impurities
Detection of water in sample- if water is present
the spectra shows three characteristic bands at
3600-3200 cm-, 1650 and 600-300 cm-
24. Measurment of paints and varnishes
• Reflectance Analysis
• Measure IR absorbance of paints on
automobiles without destroying the
surface.
• Make and year of the car can be
determined from IR spectral analysis.
25. Examination of old paintings and artifacts
• Helps to detect fake “Master pieces”
• Varnishes and paints from old monuments
can be determined by IR
• Presence of New paint traces implies that
“masterpiece” is fake.
26. In Industry
• Determine Impurities in Raw materials
• For quality control checks
• Identification of materials made in
industrial research labs e.g. impurity in
bees wax.
