Engineering Chemistry
MODULE 2
Spectroscopic Techniques And Applications
Spectroscopy deals with the interaction of atoms or molecules or matter with electromagnetic (EM) radiations.
, Engineering Chemistry
MODULE 2
• Spectroscopic Techniques And Applications
Spectroscopy deals with the interaction of atoms or
molecules or matter with electromagnetic (EM)
radiations.
All molecules possess different quantum mechanical
energy states such as Electronic, vibrational, rotational
and nuclear.
Transitions can occur between these states by absorption
or emission of EM radiations. Only those transitions that
comply with or follow quantum mechanical rules are
allowed.
Spectroscopy provides information of the details
regarding the structure and bonding.
The instrument used for spectroscopic study is called
Spectrometer.
The plot obtained from a spectrometer is called Spectra.
A spectrum provides atomic and molecular information
on the interaction of EM radiation with atoms and
molecules.
Spectroscopic study (i) Gives accurate and reliable results
(ii) Requires less time, (iii) sample unaltered.
Electromagnetic radiation is a form of energy transmitted
through space with velocity of light.(c= 3x108ms-1).
EM radiations are a bundle of radiations of different
wavelengths ranging from Gamma, X-rays, Ultraviolet, visible,
infrared and radio waves.
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, On the basis of interaction of atoms/molecules with EM
radiation, the spectra can be divided as, (i) Absorption
spectrum,(ii) Emission spectrum.
Absorption spectrum:
Atom or molecule undergo transition from lower energy state
(Ei) to a higher energy state(Ef),absorption of energy (hʋ) takes
place E.g UV visible, IR, Microwave .and NMR
Ef
hʋ
EI
Emission spectrum:
Atom or molecule undergo transition from higher energy state
(Ef) to a lower energy state (Ei),emission of energy (hʋ) takes
place. E.g Hydrogen spectrum, Atomic emission spectrum,
Atomic fluorescence spectrum.
hʋ
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, MOLECULR ENERGY LEVELS
• Electronic Energy (Eel)
• Associated with electrons of molecules, Molecular Orbital may
be bonding or antibonding, The energy gap between the
electronic energy lies in the UV-Visible region.
• Vibrational energy (Evib)
• Associated with vibration of atom/molecules about the center
of mass.The energy gap between the vibrational energy level
lies in the Infrared region.
• Rotational energy (Erot)
• Associated with rotation of atoms/molecules in space about an
axis. Possessed by molecules of gas or liquids. Energy gap lies in
the microwave region.
• Translational Energy (Etrans)
• Associated with transition of atoms /molecules with change in
center of mass.
• Etotal =Eel + E vib + Erot +ETrans and
• Eel > Evib > Erot > E Trans
• Electronic transitions are always accompanied by vibrational
and rotational transitions.
• Vibrational transitions are always accompanied by rotational
transitions.
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