This document discusses Fourier transform infrared spectroscopy (FT-IR). FT-IR uses infrared spectroscopy to identify functional groups and molecules in samples by detecting the frequencies at which they absorb infrared radiation. It provides advantages over dispersed infrared spectroscopy such as increased speed, sensitivity, and accuracy. FT-IR works using an interferometer that encodes all frequencies simultaneously before a Fourier transform separates them. This allows it to measure a full spectrum more quickly than dispersed methods. The document also outlines the basic components and working of an FT-IR instrument and describes various sampling techniques used for different types of samples.

1. Fourier Transform Infrared Spectroscopy
BY:
Gaurav Kumar Yogesh
Reg. No. CUPB/M.Sc./SBAS/PMS/2013-14/01
SUPERVISOR: DR. KAMLESH YADAV
(ASSISTANT PROFESSOR)
Centre For Physical And Mathematical Sciences
Central university of Punjab, Bathinda
M.sc. physics (weekly seminar)
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2. Content
 Introduction
 Infrared spectroscopy
 FT-IR instrument
 Working principle of FT-IR spectroscopy
 Applications of FT-IR spectroscopy
 Optical diagram of FT-IR and mathematics.
 Comparisons between Dispersed IR spectroscopy and FT-IR spectroscopy
 Sampling Techniques
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3. Introduction
 FT-IR stand for the Fourier Transform Infrared Spectroscopy.
 It is preferred method of analysing and characterising the functional
groups and molecules presents in the given samples.
 Basics principle behind the FT-IR spectroscopy is Infrared Spectroscopy.
 Infrared radiation lies between the microwave and the infrared region of
spectrum
 The wavelength of infrared radiation is greater than visible spectrum and
shorter then microwave radiation.
 The infrared radiation is divided into three categories:
1. Far-infrared - very close to the microwave radiation, wavelength 50-
1000 micrometers
2. Mid infrared-in midway of the far infrared and Near infrared, wavelength
between 2.5-50 micrometers
3. Near infrared-very close to the visible region of spectrum, wavelength
ranges from 0.78-2.5 micrometers
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4. Contd.
 The primary source of infrared radiation is thermal motion of the atoms and
molecules of objects.
 As we increase the temperature more and more numbers of atoms produce
infrared radiations.
 Even though an ice cubes can produces the infrared radiations.
 The principle behind infrared spectroscopy is
Applied Infrared Frequency = Natural Frequency of Vibrations of
molecules and atoms
 Every bond or functional groups requires different frequency for the
absorption . Hence characteristic peak is observed for the every functional
group or the part of the molecules.
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5. Infrared Spectroscopy
 For the Isopropyl alcohol CH(CH3)2OH , infrared spectroscopy identify the
several functional groups and molecules.
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Fig. FT-IR spectroscopy for the Isopropyl alcohol.

6. FT-IR Instrument Of Central University of Punjab
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7. FT-IR Spectroscopy working
 In the preferred samples the infrared radiation is passed through it, some of the
molecules and functional groups absorbs the infrared radiations of specific types
of frequency of radiations.
 Some of the infrared radiations is absorbed by the samples and some of radiations
is transmitted from the samples.
 The resulting spectrum represents the molecular absorptions and transmission,
grating , creating the fingerprints of the specific functional groups and molecules.
 Like a fingerprints no two molecules the can absorbed or transmit radiations of
same frequency, even though they have same kind of molecular structure.
 This makes the infrared spectroscopy a very useful technique of analysis of
functional group.
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8. What we gets from FT-IR Spectroscopy?
 FT-IR identify the unknown materials in the samples.
 It can provides the information of quality and consistency of samples.
 It can determine the several components in the mixtures.
 it is non-destructive technique.
 It does not requires external calibrations
 It can increase the speed, collecting the scans every seconds.
 It has greater optical throughput.
 It is mechanically very simples, with one moving part.
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9. Why FT-IR Spectroscopy is superior then IR spectroscopy
 Dispersed infrared spectroscopy is suffers from various disadvantages such as,
wavelength inaccuracies, speed and insensitivity.
 Most of radiations does not pass through the samples to the detectors. but it lost
in the narrowing slit. Which results in the poor insensitivity.
 It takes the several minutes to record the signal.
 The methods cannot applied to the fasters process, which have the higher
chemical kinetics in the seconds.
 It suffers wavelength inaccuracies due the backlash in the mechanical movement,
such as motion of the mirrors and grating.
 BUT IN THE FT-IR SPECTROSCOPY:
 FT-IR spectroscopy works on the principles of Michelson's Interferometer.
 So this method called as the Interferometric Infrared Spectroscopy.
 It can measures all the frequencies simultaneously rather than individual one.
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10. Mathematics
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• Optical path difference is
• Intensity of the detector has maxima at
and minima at

)(I
2,1,0,  nn
 )2/1(  n

11. Contd.
 The interferometer produce a special type of signal, which has all
frequencies encodes in it.
 It uses the beamspliters, which takes the incoming wave and split into
two parts.
 One reflects at the fixed mirror and other is moves to the movable
mirrors.
 The mirrors reflects from the respective mirrors and are recombined at
beamspliters.
 The resulting signal is called an interferogram which an unique property
of the every data point.
 This means that as the interferogram is measured all frequencies
simultaneously. Thus the use of interferometer is extremely very fast.
 Decoding of the individual frequency accomplished by the Fourier
transformation. This transformation is performed by the computer
devices.
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Fig. FT-IR instrument working

13. Sampling Techniques
1. Liquid samples
 Diluted solution
 Liquid cells
2. Solid samples
 Cast films
 Pressed film
 KBr Pellets
3. Gas samples
 Short path cells
 Long path cells
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14. THANK YOU
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