UNIT-V ANALYTICAL TECHNIQUES 9
Electromagnetic spectrum - absorption of radiation - electronic, vibrational and rotational
transitions - Thermal methods of analysis - TGA, DTA – Principle, instrumentation and
applications - Spectro Analytical methods - Colorimetry, IR, UV-visible spectroscopy - Principles
instrumentation and applications.
5.1 Electromagnetic spectrum (EMS)
The arrangement of all types of electromagnetic radiations in the increasing order of their
wavelength or decreasing order of their frequency is known as ‘Electromagnetic Spectrum’.
S. No. Type of radiation Wave Length(λ) Frequency (ν)
(cm) (sec-1)
1 Gamma rays 10-11 1019
2 X ray 10-9 1017
3 UV 10-7 1015
4 Visible 10-6 1014
5 IR 10-5 1013
6 Micro waves 10-3 1011
7 Radio waves (low energy) 102 106
,5.2 Principles of spectroscopy
One form of electromagnetic radiations is allowed to interact with the atoms or molecules
and the emitted, or absorbed, or transmitted or scattered radiation is analyzed. This is known as
spectroscopy.
Differences between atomic and molecular spectra
Atomic spectra Molecular spectra
1 It is simple and line spectra It is complicated and band spectra
2 It is due to electronic transition – called It is due to vibration, rotation and
electronic spectra – appear in UV – electronic transitions– appear in IR
Visible region region
5.2.1 Types of spectroscopy
When radiation meets matter, the radiation is either scattered, emitted or absorbed.so they
are of three types
a. Absorption spectroscopy
b. Emission spectroscopy
Absorption spectroscopy
In absorption spectroscopy an electromagnetic radiation (photon of energy) is absorbed
by an atom or molecule, which undergoes transition from a lower energy state to a higher energy
or excited state. The spectrum thus obtained is called the absorption spectrum.
Emission spectroscopy
If the molecule comes down from the exited state to the ground state with the emission of
photons of energy (hν). The spectrum thus obtained is called the emission spectrum.
, 5.2.2 Parameters of Spectroscopy
Electromangnetic radiation (or) Electromagnetic energy (or) Radiant energy (EMR)
Electromagnetic radiation is produced due to the interaction between the electric field and
the magnetic field. EMR is a form of energy and has both electrical and magnetic characteristics.
The electric and magnetic fields in electromagnetic wave oscillate along directions
perpendicular to the propagation direction of the wave.
Wave length (λ)
Wave length is the distance between two successive crests of a wave.
It is denoted by ‘λ’. Wave length is expressed in meters and to express very short wave
lengths nanometer (nm,10 -9 m), picometer (pm,10-12 m) or ‘non SI’ Units Angstrom (Ao,10-10 m)
Frequency (γ)
It is the number of waves crossing a point in unit time.
It is denoted by, γ
Frequency is expressed in s-1(or) Hertz, (Hz)
λ
3s-1(3Hz)
Electromagnetic spectrum - absorption of radiation - electronic, vibrational and rotational
transitions - Thermal methods of analysis - TGA, DTA – Principle, instrumentation and
applications - Spectro Analytical methods - Colorimetry, IR, UV-visible spectroscopy - Principles
instrumentation and applications.
5.1 Electromagnetic spectrum (EMS)
The arrangement of all types of electromagnetic radiations in the increasing order of their
wavelength or decreasing order of their frequency is known as ‘Electromagnetic Spectrum’.
S. No. Type of radiation Wave Length(λ) Frequency (ν)
(cm) (sec-1)
1 Gamma rays 10-11 1019
2 X ray 10-9 1017
3 UV 10-7 1015
4 Visible 10-6 1014
5 IR 10-5 1013
6 Micro waves 10-3 1011
7 Radio waves (low energy) 102 106
,5.2 Principles of spectroscopy
One form of electromagnetic radiations is allowed to interact with the atoms or molecules
and the emitted, or absorbed, or transmitted or scattered radiation is analyzed. This is known as
spectroscopy.
Differences between atomic and molecular spectra
Atomic spectra Molecular spectra
1 It is simple and line spectra It is complicated and band spectra
2 It is due to electronic transition – called It is due to vibration, rotation and
electronic spectra – appear in UV – electronic transitions– appear in IR
Visible region region
5.2.1 Types of spectroscopy
When radiation meets matter, the radiation is either scattered, emitted or absorbed.so they
are of three types
a. Absorption spectroscopy
b. Emission spectroscopy
Absorption spectroscopy
In absorption spectroscopy an electromagnetic radiation (photon of energy) is absorbed
by an atom or molecule, which undergoes transition from a lower energy state to a higher energy
or excited state. The spectrum thus obtained is called the absorption spectrum.
Emission spectroscopy
If the molecule comes down from the exited state to the ground state with the emission of
photons of energy (hν). The spectrum thus obtained is called the emission spectrum.
, 5.2.2 Parameters of Spectroscopy
Electromangnetic radiation (or) Electromagnetic energy (or) Radiant energy (EMR)
Electromagnetic radiation is produced due to the interaction between the electric field and
the magnetic field. EMR is a form of energy and has both electrical and magnetic characteristics.
The electric and magnetic fields in electromagnetic wave oscillate along directions
perpendicular to the propagation direction of the wave.
Wave length (λ)
Wave length is the distance between two successive crests of a wave.
It is denoted by ‘λ’. Wave length is expressed in meters and to express very short wave
lengths nanometer (nm,10 -9 m), picometer (pm,10-12 m) or ‘non SI’ Units Angstrom (Ao,10-10 m)
Frequency (γ)
It is the number of waves crossing a point in unit time.
It is denoted by, γ
Frequency is expressed in s-1(or) Hertz, (Hz)
λ
3s-1(3Hz)
