3. 313/12/2010 3
0.78 µm 1000 µm
IR radiation lies between the visible and microwave portions of
the electromagnetic spectrum
IR waves have wavelengths longer than visible and shorter than
microwaves
IR waves have frequencies which are lower than visible and
higher than microwaves.
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4. The energy of an electro magnetic radiation
E = hυ = hc/λ
where ,
E - energy of radiation
h - plank’s constant
υ - frequency of radiation
c- velocity of light
λ- wavelength
Frequency :- Number of compete wavelength units
passing through a given point in unit time
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5. WAVELENGTH AND WAVENUMBER
The wavelength is the distance between two successive maxima or minima
Wave number is reciprocal of wavelength
Wavelength
Length of the wave in microns (µ)
1 micron = 10-4 cm
Wave numbers
Number of waves per centimeter (cm-1)
Reciprocal Centimeter
Wavenumber (cm-1 ) = 104/Wavelength
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6. CLASSIFICATION OF SPECTROSCOPY
1. Basis of atomic or molecule level
a) atomic spectroscopy :- Changes in energy takes place at atomic level : AAS & AES
b) molecule spectroscopy :- Changes in energy takes place at molecular level
e.g.:- UV spectroscopy, colourimetry, IR spectroscopy, Fluorimetry
2) Basis of absorption or emission :-
a) Absorption spectroscopy :- where absorption of radiation is being studied
eg.:- UV spectroscopy, colorimetry, IR spectroscopy, NMR spectroscopy, atomic
absorption spectroscopy
b) Emission spectroscopy :- where study of emission radiation
Eg. Flame photometry, fluorimetry
3) Basis on electronic or magnetic level :-
Electromagnetic radiation only without the influence of
magnetic field eg . UV spectroscopy, colourimetry, Fluorimetry 6
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7. PRINCIPLE
• In any molecule it is known that atoms or group of atoms are connected
by bonds
• These bonds are analogous to springs and not rigid in nature because of
the continuous motion of the molecule
• They maintain some vibrations with some frequency characteristic to
every portion of the molecule this is called the natural frequency of
vibration
• Then energy in the from of infrared radiation is applied and when
applied frequency = natural frequency of vibration,
absorption of I.R. radiation take place and a peak is observed
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8. I.R. INSTRUMENTATION
1) I.R. Radiation sources
2) Monochromators
3) Sample cell and sampling of substances
4) I. R. Transducers/Detectors
5) Recorders
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9. Detection Electronics
and Computer
Infrared
Source
Determines Frequencies
of Infrared Absorbed and
plots them on a chart
Sample
SIMPLIFIED INFRARED SPECTROPHOTOMETER
NaCl
plates
Absorption
“peaks”
Infrared
Spectrum
frequency
intensity of
absorption
(decreasing)
focusing
mirror
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9
10. 1) I.R. RADIATION SOURCES
i) Incandescent wire source/lamp :-
- A closed wound nichrome coil
- temp 1100 0c
- near infrared region, cooling not required
ii) Nernst glower :-
- Hollow rod 1 to 3 mm diameter and 30 mm length
- temp 1000 to 1800 0c
- radiation 7100 cm-1
Requires cooling
iii) Globar sources :-
- silicon carbide rod – 50 mm length and 5 mm diameter
- temp 1300 to 17000 c
- radiation 5200 cm-1
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10
11. iv) Mercury arc :- Quartz jacketed tube, mercury vapor
at >1 atp, plasma source
- wave number > 50 cm-1
- far infrared region
v) Tungsten filament lamp :-
- for near infrared region
vi) Carbon dioxide Laser source:
It provide band of radiation in 900- 100 cm-1
range which consists of about 100 closed spaced lines,
any line can be selected by tuning the laser.
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11
12. 2) MONOCHROMATORS
i) Prism monochromator :-
• Prism used as dispersive element must be constructed of
metal halide salt
• sodium chloride is probably used
• based on high dispersion
NaCl [middle IR , 4-15µm]
KBr [far IR, 15-40µm]
Lithium fluoride, quartz [near IR]
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13. SAMPLE CELLAND SAMPLING OF SUBSTANCES
1) Sampling of Solid :-
i) Solid run in solution :-
Solid sample are usually dissolved in a non-aqueous
solvent provided there is no chemical interaction with
the solvent and also provided the solvent dose not absorb
in the studied range.
eg. Carbon tetrachloride, chloroform, alcohols, acetone,
cyclohexane .
ii) Solid films :-
Sample solution is placed on the surface of a potassium
bromide or sodium chloride and solvent is allowed to
evaporate 13
13
14. II) To run an IR spectrum of a liquid
sample, a drop sample is applied
to a salt plate. A second salt
plate is placed on top of the first
one such that the liquid forms a
thin film “sandwiched” between
the two plates.
2) Liquid Sample :
I) The sample that are liquid at
room temp. are usually put
frequently with no preparation,
into rectangular cell made of
NaCl, KBr, and their IR spectra
are obtained directly.
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15. 15
SAMPLING OF GASES
• The dried gas sample introduced into gas cell which is
made up of glass or metal cylinder of about 10 cm long
• Cell is equipped with mirrors and to bring multiple
reflection to increase effective path length
• The end wall of gas cell are made up of NaCI
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17. 1. BOLOMETER
• Are constructed from metals.
• Radiation fall on bolometer the bridge become unbalanced due to change
in electric resistance
• Amount of current flowing through galvanometer is measure of intensity
of radiation
• Germanium bolometer excellent for Far IR
• Response time is few milliseconds
Thermistors - Semiconductors device called thermistor
• Similar to bolometer
• Resistance made by fusing several metallic oxide
• They shows the negative thermal co-efficient of electrical resistance
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18. 2. GOLAY CELL
• It consists of small metal cylinder, one end of which closed by
blackened metal plate
• Other with metalized diaphragm
• A cylinder is filled with non absorbing gas like xenon
• Radiation fall on cell, metal plate is heated which causes the expansion
of gas which in turn affects the diaphragm
• This cause the change in output of cell.
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19. 3. THERMOCOUPLE
• Most commonly used, constructed based upon Wheatstone bridge
• It contain two fine wire of metal which has different thermo electrical
properties are welded with blackened gold coil
• Cold junction is kept constant temp.
• Hot junction is expose to radiation
• Two junction are at different temp. it cause a potential difference depending
on amount of radiation fall on hot Junction
• To enhance sensitivity several thermocouple are joined in series to give
thermopile
• Response time is about milliseconds
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20. 4. SEMICONDUCTOR DETECTORS
• Material are insulators
• Radiation fall on them it become conductor that cause rapid change in
electrical resistance
• Basic concept is IR photon displaces an electron in the detector
• Rapid response
• Very sensitive
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21. 5. PYROELECTRIC DETECTOR
• Pyroelectric detectors are ferroelectric devices, electrical
conductors, or semiconductors which change electric
polarization as a function of temperature .
• The degree of polarization decreases with increase in
temperature. A signal is produced at electrodes which are
placed across the surface of the detector material as small
polarization changes occur.
• Other materials such as strontium barium niobate and
especially lithium tantalite which is used commercially in
fire detectors also function as suitable detectors for IR
instruments.
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22. CONCLUSION
Infrared spectroscopy is a most important analytical techniques.
Despite of short comings it has prove to be one of the most
valuable methods for characterizing, both qualitatively and
quantitatively the multitude of organic compounds encountered
in research and industry.
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23. Reference :
Jump up to: a b Laurence M. Harwood; Christopher J. Moody (1989). Experimental organic chemistry: Principles and Practice
(Illustrated ed.). Wiley-Blackwell. p. 292. ISBN 0-632-02017-2.
• Paula, Peter Atkins, Julio de (2009). Elements of physical chemistry (5th ed.). Oxford: Oxford U.P. p. 459. ISBN 978-0-19-
922672-6.
Soran Shadman; Charles Rose; Azer P. Yalin (2016). "Open-path cavity ring-down spectroscopy sensor for atmospheric
ammonia". Applied Physics B. 122: 194. Bibcode:2016ApPhB.122..194S. doi:10.1007/s00340-016-6461-5.
Jump up to: a b Chromatography/Fourier transform infrared spectroscopy and its applications, by Robert White, p7
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