1. RAKHI.R 14308015 1st YEAR MSc MICROBIOLOGY PONDICHERRY
UNIVERSITY INFRARED SPECTROSCOPY
2. INTRODUCTION Infrared radiation = 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
16. 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
17. 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
18. 3. Monochromators convert polychromatic light into
monochromatic light. They are of 3 types. a) metal halide prisms b)
NaCl prisms c) gratings
19. convert the radiation into electrical signal. Two Types Of
Detectors 1. Photon detector 2. Thermal detector 4. DETECTOR
20. Applications Compositional analysis of organic, inorganic
and polymers. Detection of Impurities.
21. Biological and biomedical fields like detection of water in
biological membranes. Analysis of Aircraft exhausts Measurement of
toxic gas in fuels Combustion Gas analysis
22. Easy to use Inexpensive , found in most labs. Analysis time
typically < 10 minutes ADVANTAGES:
23. Sensitive to the absorption of water . If there is
significant moisture in the sample the penetration distance of the
light decreases. DISADVANTAGES:
