1. Satish Pradhan Dnyanasadhana College, Thane
Department of Chemistry T.Y.B.Sc. Analytical Chemistry Paper-IV Sem-V UV-Visible spectroscopy

2. Contents 4.2 Molecular Spectroscopy – III (04 L)
4.2.1 Recapitulation of basic concepts
4.2.2 Instrumentation, Principle and working of single and double beam spectrophotometers.
4.2.3 Applications of UV- Visible Spectrophotometery

3. 4.2.1 Recapitulation of basic concepts
What is Electromagnetic Radiation
Electromagnetic radiation, or light, is a form of energy whose behavior is described by the properties of both waves and particles. The optical properties of electromagnetic radiation, such as diffraction, are explained best by describing light as a wave.

4. Properties of electromagnetic radiation
Frequency: The number of oscillations of an electromagnetic wave per second (n).
Wavelength: The distance between any two consecutive maxima or minima of an electromagnetic wave (l).
Wave number: The reciprocal of wavelength (–n).

5. The electromagnetic spectrum
The electromagnetic spectrum consists of radiation that ranges in wavelength from m (high energy) to 104 m (low energy). The physical principles and mathematical description of radiation across the whole of the electromagnetic spectrum is the same, however, it is convenient to divide it into a number of different regions depending on the origin of the waves, i.e., cosmic rays, gamma rays, x-rays, ultraviolet, visible, infrared, microwaves, and radio waves.

6. Energy Increases
Wavelength Decreases
Electromagnetic Spectrum

7. In this energy is supplied by photons.
Sources of Energy
In this energy is supplied by photons.
Absorption
Spectroscopy
Scattering
Techniques

8. Thermal or chemical energy source .
Sources of Energy
Thermal or chemical energy source .
Emission
Spectroscopy
luminescence spectroscopy

9. Quantum theory of Radiation
Black Body
White Body

10. Energy for Atom and Molecule
Electronic Energy
Electronic Energy
Atom
Atom
Rotational Energy
Vibrational Energy

11. Electronic Energy of Molecule*
Antibonding *
Antibonding ∏
n *
 *
n *
 * n
Nonbonding 
Bonding
Energy 
Bonding

12. ELECTRONIC TRANSITIONS
, , and n electrons
d and f electrons
charge transfer electrons
Organic Molecule
Inorganic molecule
Organic +
Inorganic

13. Electromagnetic spectrum
Radiation Source
H2 and D2 lamp
Wavelength region
continuum source from 160–380 nm
Useful for UV
molecular absorption
UV Spectroscopy

14. Electromagnetic spectrum
Radiation Source
Tungsten lamp
Wavelength region nm
Useful for
Vis molecular absorption
Visible Spectroscopy

15. Light get reflected back
Scattering of Light
Transmission of light
0.003
Absorbance
Light get reflected back

16. Regions of Absorption
U.V. nm
Visible nm

17. INSTRUMENT
Colorimeter OR
Photometer nm
Spectrophotometer
nm.

18. 4.2.2 Instrumentation, Principle and working of single and double beam spectrophotometers.

19. Light Dispersing devices
Instrumentation,
Radiation Source
Light Dispersing devices
Sample Cells
Detectors
Readout Device

20. Electromagnetic spectrum
Radiation Source
H2 and D2 lamp
Wavelength region
continuum source from 160–380 nm
Useful for UV
molecular absorption
UV Spectroscopy

21. Electromagnetic spectrum
Radiation Source
Tungsten lamp
Wavelength region nm
Useful for
Vis molecular absorption
Visible Spectroscopy

22. LIGHT DISPERSING DEVICES MONOCHROMATORS SPECTROPHOTOMETERS
FILTERS
(COLORIMETERS )
MONOCHROMATORS SPECTROPHOTOMETERS

23. Filter: A filter transmits the monochromatic beam of light and absorbs other light
Polychromatic light
Monochromatic light

24. FOCUSING LENS COLLIMATING LENS PRISM ENTRANCE SLIT EXIT SLIT
LAMBDA-1
LAMBDA-2
PRISM
ENTRANCE SLIT
EXIT SLIT
PRISM MONOCHROMATOR

25. MAGINIFIED VIEW
ENLARGED VIEW
GRATING MONOCHROMATOR

26. Sample Cells
Rectangular
Cylindrical

27. PHOTO CELL
DETECTOR
Detectors:-
PHOTO
MULTIPLIER
TUBE
PHOTOTUBES

28. Semiconductor Selenium B
PHOTOCELL DETECTOR
(--) D D G C E- G B A +
Iron plate A
Semiconductor Selenium B
Thin layer of silver C

29. Construction: It consists of Iron plate A on which a thin layer of a semiconductor like Selenium B is deposited. The layer is covered by very thin layer of silver C that acts as collector electrode. A ring D can hold the silver plate in its place.
Working:-This cell operates without battery. When the transmitted beam of light passes through thin film of silver metal to selenium layer, electrons released from semiconductor surface .These electrons pass through a hypothetical barrier layer in between silver and selenium layer and are collected by silver electrode.
Thus under the action of light a cell is formed with iron plate as positive electrode
Metal ring as negative electrode. The current flow is detected in galvanometer. This current is directly proportional to absorbance.

30. PHOTO TUBE DETECTOR - AMPLIFIER RECORDER Collector Anode (+)
Photo Cathode (-)
Collector Anode (+) -
AMPLIFIER RECORDER

31. PHOTOMULTIPLIER TUBE DETECTOR

32. Signal Processors
The electrical signal generated by the transducer is sent to a signal processor where it is displayed in a more convenient form for the analyst.
Examples of signal processors include analog or digital meters, recorders, and computers equipped with digital acquisition boards.
The signal processor also may be used to calibrate the detector’s response, to amplify the signal from the detector, to remove noise by filtering, or to mathematically transform the signal.

33. Instruments

34. SINGLE BEAM SPECTROPHOTOMETER
Radiation Source
Collimating Lense
O.2
Read out Meter Amplifier PMT Detector Sample Cuvette Grating
SINGLE BEAM SPECTROPHOTOMETER

35. DOUBLE BEAM SPECTROPHOTOMETER
PMT Detector
Blank Cuvette
Mirror
Grating Tungsten Lamp
Read
Out
Meter
Mirror
Sample Cuvette
Mirror Deuterium Lamp
PMT Detector
DOUBLE BEAM SPECTROPHOTOMETER

36. Distinguish Between Photometer and Spectrophotometer
Radiation source is Tungsten filament lamp.
Absorbance of light is measured in the wavelength nm.( Visible region)
Filters are used to select monochromatic light.
Sample cells made from glass.
Detectors used are photocell or photoemmisive tube.
Absorbance of coloured solution is measured
SPECTROPHOTOMETER.
Radiation source is Hydrogen or deuterium lamp.
Absorbance of light is measured in the wavelength nm. (U.V.& Visible region)
Prism or Gratings are used to select monochromatic light.
Sample cells made from quartz.
Detectors used are photomultiplier tube.
Absorbance of coloured as well as colorless solution can be measured

37. Applications of U.V. & Visible Spectroscopy
Qualitative Analysis
Identification of Structural Groups in Molecules.
Spectroscopic analysis of a substance is carried out using radiation of a particular wavelength this wave length is called as Lambda Max. The Constituent groups in a molecule absorbed to their characteristic wavelengths.
It is possible to determine a particular group in a molecule by determining its Lambda Max. Lambda Max values of important groups are given in following table.

38. A B S O N C E Wavelength --- 200 300 400 500 600 700 800
The Wavelength at which absorbance of highly
concentrated solution is maximum is called as Lambda max. A B S O N C E
Lambda Max
Wavelength ---

39. Orbital's containing electrons are called as Bonding Orbital's
Types of Orbital's
Bonding Orbital's :
Orbital's containing electrons are called as Bonding Orbital's
Antibonding Orbital's vacant or unounoccupied Orbital's ( Not containing electrons) are called as anti Bonding Orbital's .

40. Closed shell electrons Covalent single bonded electrons
Types of Electrons in
a molecule
Closed shell electrons
Not absorbing /
Not in bonding
Covalent single bonded electrons
σ Sigma
Electrons in
π orbital's
Paired nonbonding outershell electrons
n electrons
C---C
Sigma bond
σ Sigma electrons
C==C
C C
H—O---H

41. The three include transitions involving
ELECTRONIC TRANSITIONS
There are three types of electronic transitions.
The three include transitions involving
1) , , and n electrons (Organic Molecule)
2) d and f electrons (Inorganic molecule)
3) Charge transfer electrons.(Org+Inorgainc)

42. ELECTRONIC TRANSITIONS
, , and n electrons
d and f electrons
charge transfer electrons
Organic Molecule
Inorganic molecule
Organic +
Inorganic

43. Energy levels for Electronic transitions in
a Molecule *
Antibonding *
Antibonding ∏
n *
 *
n *
 * n
Nonbonding 
Bonding
Energy 
Bonding

44. Example Functional Groups Lambda Max ( nm) Solvents Acetic Acid --COOH
208
Ethyl Alcohol
Acetyl Chloride
--COCl
220
Hexane
Acetamide
--CONH2
178
Nitromethane
--NO2
201
Methyl Alcohol
Azomethane
--N=N--
338
Acetaldehyde
>C=O
290
Acetone
189

45. B) Chromopores and Auxochromes:
Chromopores are unsaturated groups responsible for the absorption of visible light.e.g. >C=O (carbonyl group). The molecule which contain Chromopores are called as chromogen and the colour of the compound is due to unsaturated groups present in Chromopore.
The intensity of the colour of the chromogen increases with the number of chromophores present.
For ex.ethylene (CH2= CH2) is colorless but CH3-( CH= CH)6--CH3 is yellow. As the number of groups increase in a molecule absorption shifts to longer wavelength and the colour deepens.

46. Example Functional Groups Lambda Max ( nm) Solvents Ethylene
>C=C<
171
Vapour
Acetaldehyde
>C=C
290
Hexane
Acetic Acid
--COOH
208
Ethyl Alcohol
Nitromethane
--NO2
201
Napthalene
Unsaturated comp.
275
Methyl Vinyl Ketone
215
Cinnamic Acid

47. Applications of U.V. & Visible Spectroscopy
Quantitative Analysis By Calibration Curve Method

48. Other Applications
UV and visible spectroscopy can be used up to concentrations up to and some times up to 10-7 M .
Qualitative analysis can be performed because each absorbing species absorb at different wave length.
It used in water and air pollution studies.
It is also used to study the complexes and in the determination of complex.
It is used in industry to monitor various process controls.
It is also used to study to distinguish between cis-and trans isomerism.
C- is isomer absorbs at shorter wave length and trans isomer absorb at longer wave length.

49. Thank you