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UNIT-5
SPECTROSCOPIC TECHNIQUES AND
APPLICATIONS
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CONTENTS
• What is Spectroscopy?
• Types of spectroscopy
• Uses and Applications
• Conclusion
• Reference
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WHAT IS SPECTROSCOPY?
• Spectroscopy deals with the interaction of
electromagnetic radiation with matter
• Used to extract very useful information like
structural and other physico-chemical
properties of molecules.
• Spectroscopy is the most imperative and
promising tool for the structural investigation
of chemically relevant systems.
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THE INTERACTION OF RADIATION WITH MATTER
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Electromagnetic Spectrum
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• Electromagnetic radiations are produced by the
oscillations of electric and magnetic dipoles
residing in the atom.
• The most important consequence of
electromagnetic interaction is that energy is
absorbed or emitted by the matter in discrete
amounts called quanta.
• Spectroscopic methods are generally used to
measurer the energy difference between various
molecular energy levels and to determine the
atomic and molecular structures.
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Electromagnetic waves travel at the speed of light and their
frequency and wavelength can be determined by the formulas:
where 'c' is the speed of light in meters per
second,
lambda λ is the wavelength in meters
frequency is in cycles per second.
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Molecule contains :
• Translational energy
• Rotational energy
• • Vibratioal energy
• Electronic energy
• All except the Translational energy are quantized
• Energy(molecule )= E(rot )+ E(vib )+ E(elec )
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THE INTERACTION OF RADIATION WITH MATTER DEPENDS UPON BOTH
RADIATION PROPERTIES AND STRUCTURAL PARTS OF THE MATERIALS
INVOLVED. THIS INTERACTION BETWEEN MATTER AND RADIATION LEADS TO
A VARIETY OF SPECTRA.
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THREE TYPES OF THE ABSORPTION SPECTRUM:
Nuclear spin states
Electronic energy levels
Infrared
Radio frequency
Ultraviolet-
visible
Absorptionof
Electromagnetic
Radiation Results
inTransition Between
Region ofthe
Electromagnetic
Spectrum
Nuclear magnetic
resonance
Infrared
Ultraviolet-
visible
Type of
Spectroscopy
Frequency
(hetz)
2.5 x1014-1.5x1015
3 x107-9x108
1 x1013
-1x1014 Vibrational energy levels
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INFRARED SPECTROSCOPY
Far-Infrared (400-33 cm-1): vibrations
of molecules containing heavy
atoms, molecular skeleton
vibrations and crystal lattice
vibrations
Mid-Infrared (4000-400 cm-1): useful
for organic analysis
Near Infrared (12820-4000 cm-
1): overtones; very useful for
quantitative analysis
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REQUIREMENTS FOR VISIBILITY IN THE IR REGION
(selection rules)
• A change in dipole moment, whether it is induced
or permanent.
Heteronuclear Diatomicmlecules E.g HCl, HBr etc
N2, F2, etc. are inactive in the IR.
• Resonant frequencies that are in the infrared
frequency range of 100−4000 cm−1.
• After the absorption of radiation only transition for
which v=(+)(-) i.e, transition from=0 to V=1(change
in vibration quatum number between two vibrational
energy levels)
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Molecular Vibrations
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CHANGE IN DIPOLE MOMENT IN
TRIATOMIC MOLECULES
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Hooke’s Law
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IR SPECTRUM
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Infrared Spectroscopy
Infrared spectrum of 3-methyl-2-butanone.
• Infrared spectrum of 3-methyl-2-butanone.
Fingerprint Region:
Highly Complex and Unique for Every
Molecule
C-H Stretching
C=O Stretching
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UV spectrum of acetone
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