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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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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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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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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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.

FT-IR Instrument Of Central University of Punjab

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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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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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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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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

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

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Fig. FT-IR instrument working

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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THANK YOU

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