•Introduction• Nature of radiation• Electromagnetic Spectrum• Types of Spectroscopy • Principle of Absorption Spectroscopy• Law’s of light absorbance• Representation of spectral data• Spectrophotometer

1. Spectroscopy
Dr. J. Kashanna
Assistant Professor,
Department of Chemistry,
Rajiv Gandhi University of Knowledge Technologies-Basar,
Nirmal, Telangana-504107, India.
Email: jajulakashanna@yahoo.co.in, jajulakashanna@rgukt.ac.in

3. Spectroscopy is study of interaction of electromagnetic radiation with matter
n = 1
n = 2
hv
+
EMR
EMR
Particle/Matter

4. Eg
Ee
Excitation
Absorption
Eg
Ee
de-excitation
Emission
hv
The interaction of electromagnetic radiation with matter takes place by two
ways, viz., 1. Absorption 2. Emission and 3. Scattering
Advatages:
1. Takes less time.
2. Requires small amount of compound.
3. Conveys highly reliable information.
4. Continuous operation is often possible.
They help in the study of matter with respect to
1. qualitative study
2. quantitative study:

5. The nature of radiation:
1. EM is a form of energy that is all around us.
2. EM is a form of energy and has both electrical and magnetic
characteristics.
3. The electric and magnetic fields in an electromagnetic wave oscillate
along directions perpendicular to the propagation direction of the wave.

6. 1. Frequency : The number of times a waves passed through a given point in one
second (measured in Hz).
• Wavelength (λ) : The distance between two successive waves (measured in m).
• Amplitude: It is the maximum distance a wave extends beyond its middle
position.
• Velocity: The distance travelled by the wave in one second (measured in m/s).
Characteristicks:

7. The arrangement of various types of electromagnetic radiation in order of
their increasing wavelengths.
Electromagnetic Spectrum:

9. Principle of Spectroscopy:

11. The effect of electromagnetic radiation on interaction with matter depends on energy
associated with the radiation
• Very energetic radiations (UV and x-ray) may cause an electron to be
ejected from the molecules
• Radiation in the infrared region of the spectrum have much less
energy they can cause vibrations in molecules
Interaction with matter:

12. S. No EM Possible transition Types of
spectroscopy
1 ‫ץ‬ Nuclear Nuclear
2 X-Ray Inner electron XRD
3 UV Outer electron UV-Vis
4 NIR Outer e- +
molecular
vibrations
IR
5 IR Molecular
vibrations
Pure IR
6 Microwave Molecular rotations
+ nuclear spin flips
Microwave
7 Radio waves Nuclear spin flips Resonance
spectroscopy

13. Types of Spectroscopy:
When radiation meets matter, the radiation is either scattered, emitted or absorbed .
So, they are of three types
1.Absorption spectroscopy
2.Emission spectroscopy
3. Scattering spectroscopy

14. Absorption spectroscopy:
In absorption spectroscopy an electromagnetic radiation is absorbed by an atom or
molecule which undergoes transition from a lower energy state to a higher energy or
excited state
Absorption occurs only when the energy of radiation matches the
difference in energy between two energy levels
Eg
Ee
Excitation
Absorption

15. Emission spectroscopy:
Atoms or molecules that are excited to high energy levels can decay to lower levels
by emitting radiation
The substance first absorbs energy and then emits this energy as light
Emission can be induced by sources of energy such as flame or electromagnetic
radiation
Eg
Ee
de-excitation
Emission
hv

16. Scattering spectroscopy:
Scattering spectroscopy measures certain physical properties by measuring the
amount of light that a substance scatters at certain wavelenths .
One of the most useful applications of light scattering spectroscopy is RAMAN
SPECTROSCOPY

17. Principles of absorption spectroscopy:
Eg
Ee
Excitation
Absorption
hv
When a chemical compound is irradiated with EMR, transition takes place from lower
energy state to higher energy state
∆E = hv
⊽ = ∆E/hc
Where, h = Plancks constant

18. A molecule in space can have many sorts of energy by virtue of various kinds of
motions and other kind of interactions, viz.,
1. Translation motion
2. Rotational motion
3. Vibrational motion
4. Electronic motion
The internal energy of a molecule may be considered to be sum of electronic,
vibrational, rotational and translational energies.
Therefore, Eint = Eele + Evib + Erot + Etrans
The internal energy of the molecule is quantised, so that the molecule may be
regarded as possessing certain discrete energy states.

20. Lamberts law:
• It states that when monochromatic light passes through a transparent medium, the
intensity of transmitted light decreases exponentially as the thickness of absorbing
material increases
Therefore, -dI/dx ∞ I
-dI/dx = kI
-dI/I = kdx
Where, I = Intensity of radiation after passing through the thickness x
dI = decrease in intensity on passing through the small thickness dx
k = absorption coefficient
On integrating both sides and simplying,
-lnI/Io =kx
-2.303logI/Io = kx
logIo/I = kx/2.303
A = k’x
Units of k or K’
cm-1 or m-1

21. Beer’s law:
• It stats that the intensity of transmitted monochromatic light decreases
exponentially as the concentration of the absorbing substance increases
Therefore, -dI/dx ∞ IC
-dI/dx = €IC
-dI/I = € dxC
Where, I = Intensity of radiation after passing through the thickness x
dI = decrease in intensity on passing through the small thickness dx
€ = molar ectinction coefficient
C = Concentration of solution in moles/litre
On integrating both sides and simplying,
-lnI/Io = € xC
-2.303logI/Io = € xC
logIo/I = € Cx/2.303
A = €’xC
Units of k or K’
Litre. moles-1 cm-1 or Litre. moles-1 m-1

22. Presentation of spectral data:

23. Spectrophotometer:
A spectrophotometer is an instrument that measures the amount of light
absorbed by a sample.
• used to measure the concentration of solutes in solution by measuring the
amount of the light that is absorbed by the solution in a cuvette placed in
the spectrophotometer .

24. Questions ?????