1. RAKHI.R
14308015
1st YEAR MSc MICROBIOLOGY
PONDICHERRY UNIVERSITY
INFRARED SPECTROSCOPY

2. INTRODUCTION …
 Infrared radiation
λ = 700 nm – 1 mm
f = 430 THz – 300 GHz

3. IR SPECTROSCOPY:
 The study of absorption of infrared radiation, which causes
vibrational transition in the molecule.
 Vibrational spectroscopy.
 Mainly used in structure elucidation to determine the functional
groups.

4. PRINCIPLE:
 Molecules are made up of atoms linked by chemical bonds.
The movement of atoms and the chemical bonds is like spring
and balls (vibration).
 This characteristic vibration are called Natural frequency of
vibration.

5.  When energy in the form of infrared radiation is applied then
it causes the vibration between the atoms of the molecules.
 Applied infrared frequency = Natural frequency of vibration,
Absorption of IR radiation takes place, a peak is observed.
 Different functional groups absorb characteristic
frequencies of IR radiation, gives the characteristic peak
value.
 IR spectrum of a chemical substance is a finger print of a
molecule for its identification.
Principle ...

6. Molecular vibrations
Stretching vibrations Bending vibrations
Symmetrical Asymmetrical In plane Out plane
scissoringscissoring rocking wagging twisting

7. 1. Stretching vibrations:
 Vibration or oscillation along the line of
bond
 Change in bond length

8. a) Symmetrical stretching:
 Two bonds increase or decrease in length simultaneously.
H
H
C

9. b) Asymmetrical stretching
 one bond length is increased and other is decreased.
H
H
C

10. 2. Bending vibrations
• Vibration or oscillation not along the line of bond
• Deformations
• Bond angle is altered

11. A) In plane bending
i. Scissoring:
 2 atoms approach each other
 Bond angles are decrease
H
H
CC

12. ii. Rocking:
 Movement of atoms take place in the same direction.
H
H
CC

13. B) Out plane bending
i .Wagging:
Two atoms move to one side of the plane. They move up and
down the plane.
ii. Twisting:
One atom moves above the plane and another atom moves
below the plane.
H
H
CC
H
H
CC

14. INSTRUMENTATION:
 2 types - IR frequencies are handled.
1) dispersive type -
IR is separated into individual frequencies by
dispersion, using a grating monochromator.
2) interferometric type (FTIR) -
IR frequencies are allowed to interact to produce an
interference pattern and this pattern is then analyzed,
to determine individual frequencies and their
intensities.

15. The main parts of IR spectrometer are as follows:
1. Radiation source
2. Sample cells and sampling of substances
3. Monochromators
4. Detectors

18. 1.IR source
 Globar -
 W filament lamp
 Nernst Glower -Composed of rare earth oxides
(Zirconia, Yttria & Thoria )
 Special high pressure Hg arc lamp
 CO2 laser
silicon carbide

19. • Made up of alkali halides like NaCl or KBr .
• Aqueous solvents cannot be used -they dissolve alkali
halides.
• Only organic solvents like chloroform is used.
• IR spectroscopy has been used for the characterization of
solid, liquid, gas samples
2. SAMPLE CELL

20. 3. Monochromators
 convert polychromatic light into monochromatic light.
 They are of 3 types.
a) metal halide prisms
b) NaCl prisms
c) gratings

21.  convert the radiation into electrical signal.
 Two Types Of Detectors
1. Photon detector
2. Thermal detector
4. DETECTOR

22. Applications
• Compositional analysis of organic, inorganic and polymers.
• Detection of Impurities.
•

23. • Biological and biomedical fields like detection of water in
biological membranes.
• Analysis of Aircraft exhausts
• Measurement of toxic gas in fuels
• Combustion
• Gas analysis

24.  Easy to use
 Inexpensive , found in most labs.
 Analysis time typically < 10 minutes
ADVANTAGES:

25.  Sensitive to the absorption of water . If there is significant
moisture in the sample the penetration distance of the light
decreases.
DISADVANTAGES:

26. Summary:
 Electromagnetic radiation
 Principle
 Molecular vibration
 Instrumentation
 Application
 Advantages
 Disadvantages

27. Reference:
• Principles and Techniques of Biochemistry &Molecular
biology(7thedition) –Keith Wilson & John walker
• www.google.com