In this presentation, I mentioned Principles, Vibration, Potential energy diagram , Harmonic Oscillator, Vibration mode, instrumentation and application of IR spectroscopy . I referred Principles of Instrumental analysis, Seventh edition, Skoog, Holler and crouch. Once you read this Presentation you will get clear point about IR spectroscopy.
2. CONTENT
This is for Your’s time…
IR Spectroscopy
Dipole Moment Changes
during Vibrations and Rotations
Types of Molecular Vibrations
Potential-energy diagram
Selection Rules
Vibrational Modes
IR Instrumentation
Summary
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3. What is the purpose of using IR?
What is Spectroscopy ?
What is Electromagnetic radiation ?
This is for Your’s time…
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What is the principle of IR spectroscopy?
4. The infrared (IR) region of the spectrum encompasses radiation with wavenumbers
ranging from about 12,800 to 10 cm21 or wavelengths from 0.78 to 1000 µm.
The IR spectrum is usually subdivided into three regions,
NEAR IR
MIDDLE IR
FAR IR
IR SPECTROSCOPY
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5. Dipole Moment Changes during Vibrations and Rotations
Heteronuclear diatomic molecules are IR Active ?
Homonuclear species are IR Inactive ?
Types of Molecular Vibrations
Two types of Vibrations
Stretching Vibration
Bending Vibration
The relative positions of atoms in a molecule are not fixed but instead fluctuate continuously Why?
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6. Stretching Vibrations
Symmetric Vibrations
Asymmetric Vibrations
Bending Vibrations
In plane rocking
In plane scissoring
Out of plane wagging
Out of plane twisting
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10. Selection Rules
Δ𝜈 = ±1
Vibrational Modes
For a linear molecule is given by 3N-5
For a Non-linear molecule is given by 3N-6
Four factors tend to produce fewer experimental bands than would be expected from the theoretical
number of normal modes.
The symmetry of the molecules .
The energies of two or more vibrations are identical or nearly identical.
The absorption intensity.
The vibrational energy. 10
11. How many vibrational modes are possible for CO2 ?
Why is it that although the CO2 molecule has four vibrational modes only two peaks are seen on
its IR spectrum?
How many vibrational modes of CO2 are IR active?
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12. IR Instrumentation
Three types of instruments for IR absorption measurements are commonly available:
(1) Dispersive spectrophotometers with a grating monochromator
(2) FT spectrometers employing an interferometer
(3) Nondispersive photometers using a filter or an absorbing gas that
are used for analysis
FT spectrometer type of instrument has been largely displaced for mid- and far-IR
measurements – Why?
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IR Sources
The Nernst Glower
The Globar
Incandescent Wire Source
The Mercury Arc
The Tungsten Filament Lamp
The Carbon Dioxide Laser Source
Semiconductor IR Laser Sources
18. Very high-resolution work that is encountered with gaseous mixtures having
complex spectra resulting from the superposition of vibrational and rotational
bands.
The study of samples with high absorbances.
The study of substances with weak absorption bands.
Investigations requiring fast scanning such as kinetic studies or detection of
chromatographic effluents.
Collecting IR data from very small samples.
obtaining reflection spectra.
IR emission studies.
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Advantages of FT Spectrometers
19. SUMMARY
The infrared (IR) region of the spectrum encompasses radiation with wavenumbers ranging from
about 12,800 to 10 cm21.
The IR spectrum is usually subdivided into three regions, the near-IR, the mid-IR, and the far-IR.
IR inactive-No net change in dipole moment occurs during the vibration or rotation of
homonuclear species such as O2, N2, or Cl2.
The selection rule states that Δ𝜈 = ±1.
Three types of instruments for IR absorption measurements are commonly available:
Dispersive spectrophotometers with a grating monochromator,
FT spectrometers employing an interferometer and
Nondispersive photometers using a filter or an absorbing gas that are used for analysis of
atmospheric gases at specific wavelengths.
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