1. INFRARED
SPECTROSCOPY
-By,
Revti Lohey.

2. overview
 Introduction to IR Spectroscopy
 Basic principle of IR Spectroscopy
 Instrumentation
 Modes of vibration
 Stretching vibration
 Bending vibration
 Absorption bands
 Application

4. INTRODUCTION
 Infrared spectroscopy (IR spectroscopy) is
the spectroscopy that deals with the infrared
region of the electromagnetic spectrum, that
is light with a longer wavelength and
lower frequency than visible light.
 As with all spectroscopic techniques, it can
be used to identify and study chemicals.

5.  The infrared portion of the electromagnetic
spectrum is usually divided into three
regions; the near-, mid- and far- infrared,
named for their relation to the visible
spectrum.
REGION WAVELENGTH
RANGE (MICRO M.)
WAVELENGTH NO.
(1/cm)
NEAR 0.78-2.5 12800-4000
MIDDLE 2.5-50 4000-200
FAR 50-1000 200-10

6. Basic principle
 IR radiation does not have enough energy to
induce electronic transitions as seen with
UV.
 Absorption of IR is restricted to compounds
with small energy differences in the possible
vibrational and rotational states.
 For a molecule to absorb IR, the vibrations or
rotations within a molecule must cause
a net change in the dipole moment of the
molecule

7.  The alternating electrical field of the
radiation interacts with fluctuations in the
dipole moment of the molecule.
 If the frequency of the radiation matches
the vibrational frequency of the molecule
then radiation will be absorbed, causing a
change in the amplitude of molecular
vibration.

8. instrumentation

9. IR spectrometer
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10.  Frequencies absorbed by the molecules
depends upon the characteristic of their
structure.
 These absorptions are called resonant
frequencies, i.e. the frequency of the
absorbed radiation matches the transition
energy of the bond or group that vibrates.

11.  Vibration falls in two main categories:
1. Stretching vibration- Change in inter-
atomic distance along bond axis.
2. Bending vibration- Change in angle
between two bonds.
 They can be further categorized as:
symmetric and anti-symmetric stretching
(in stretching vibration) & scissoring,
rocking, wagging and twisting (in bending
vibration)

12. Stretching vibration
 Symmetrical stretching.
 Anti-symmetrical stretching.

13. Bending vibration
 Rocking.
 Scissoring.
 Wagging.
 Twisting.

14. Absorption bands

16. applications
 Widely used in organic chemistry.
 Used for the analysis of complex bio-molecules such
as proteins, lipids and nucleic acids.
 It can be used to determine molecular structure.
 It studies the progress of reaction (disappearance of
characteristic absorption band)
 Analysis of multilayered polymeric film.
 Identification of functional group.

17.  Used to study isomerism in organic chemistry
 In industry, for quality control check, to
determine the percent of required product.
 Detection of impurities.
Ex. Ketone impurity in alcohol.
 Used for the characterization of the
heterogeneous catalyst.
 Used for analysis of petroleum, oil & grease.
 Examination of old paintings and artifacts.

18. Thank you. 