The document discusses infrared (IR) spectroscopy. It explains that IR spectroscopy analyzes molecular vibrations and rotations that are excited when molecules absorb IR radiation. The experimental setup for IR spectroscopy includes an IR source, fore optics to direct the beam at the sample, a monochromator to separate wavelengths, a detector to measure absorption, and a recorder to display the results. Molecular vibrations that can be measured include stretching and bending vibrations of bonds that change the molecule's dipole moment.

1. MOHAMED NIJAS V
S5
I.S.P

2. CONTENT
 SPECTROSCOPY.
 IR SPECTROSCOPY.
 MOLECULAR VIBRATIONS.
 EXPERIMENTAL SETUP.
 FUTURE DIRECTIONS.

3. SPECTROSCOPY???
 Method of “Seeing the unseeable”
 Using electromagnetic radiation to obtain
information about atoms and molecules that are
too small to see.
Atoms
Molecules
E
M
R

4. Spectroscopy is an instrumentally aided study of
the interactions between matter (sample being
analyzed) and energy (any portion of the
electromagnetic spectrum)
EMR ANALYTE SPECTROPHOTOGRAPH
1.UV-Visible radiations--------excitation of electrons---------UV-visible spectrum
2.IR-radiations------------------vibration changes in electrons--------IR spectrum
3.Radio frequency---------------spin rotational changes-------------N.M.R spectrum
Conc. should be lower

5. IR SPECTROPHOTOMETRY
Energy of molecule = Electronic energy+
Vibrational energy + Rotational energy
 Concerned with the study of absorption of infrared
radiation, which causes vibrational transition in the
molecule.
 Thus known as Vibrational spectroscopy.
 Mainly used in structure elucidation to determine
the functional groups.

6. Most of the analytical applications are confined to the
middle IR region because absorption of organic
molecules are high in this region.
IR region: 0.8
µm (800nm) to
1000 µm (1mm)
Near IR: 0.8-2
µm
Middle IR: 2-15
µm
Far IR: 15-1000
µm

7. PRINCIPLE OF IR SPECTROSCOPY
 Molecules are made up of atoms linked by chemical bonds.
The movement of atoms and the chemical bonds look like
spring and balls (vibration).
 This characteristic vibration are called
Natural frequency of vibration.
 Applied infrared frequency = Natural frequency of vibration
 Change in dipole moment is required

8. MOLECULAR VIBRATIONS
Bending vibrationsStretching vibrations
 Vibration or oscillation
along the line of bond
 Change in bond length
 Occurs at higher energy:
4000-1250 cm-1
a) Symmetrical stretching
b) Asymmetrical stretching
•Vibration not along the
line of bond
•Bond angle is altered
•Occurs at low energy:
1400-666 cm-1
a) In plane bending
b) Out plane bending

9. a) Symmetrical stretching:
2 bonds increase or decrease in length simultaneously.
H
H
C
STRECHING VIBRATIONS

10. b) Asymmetrical stretching
 in this, one bond length is increased and other is decreased.
H
H
C

11. a) In plane bending
i. Scissoring:
 2 atoms approach each other
 Bond angles are decrease
H
H
CC

12. ii. Rocking:
 Movement of atoms take place in the same direction.
H
H
CC

13. b) Out plane bending
i. Wagging:
 2 atoms move to one side of the plane. They move up and down
the plane.
ii. Twisting:
 One atom moves above the plane and another atom moves
below the plane.
H
H
CC
H
H
CC

14. EXPERIMENTAL SETUP

15. COMPONENTS
1. Source
2. Fore optics
3. Monochromator
4. Detector
5. Recorder

16. SOURCE
•Ideal => black body radiator
•COMMONLY USED =>globar FILAMENT &NERNST GLOWER
•Globar- resistance rod of silicon carbide
•Nernst glower-a spindle of rare earth
oxide(thorium,zirconium,etc)
•Globar-for longer wavelengths
•Nernst glower-for shorter wavelengths

17. FORE OPTICS
•CONSISTS OF SOURCE,MIRRORS
M1,M2 AND A ROTATING MIRROR M
•M1,M2 DIVIDES THE BEAM
•M ALTERNATELY ALLOWS
THESAMPLE BEAM AND
REFERENCE BEAM TO PASS
THROUGH

18. MONOCHROMATOR
 Splits the polychromatic readiation to component
wavelengths.
 Make use of prisms or grating or both.
 Resolution depends on slit width and quality of mirrors.
 Rock salt prism is generally use d in the range of 650-
4000cm-1

19. DETECTOR
•Measure the radiant energy by its heating effect.
•Thermopiles bolometer and golay cells are generally used
•Photoconductivity is also used.
•Radiation is allowed to fall on photo conducting material and the
conductivity of the material is measured continuously by a bridge network.
•Once the sample absorbs radiation, there will be inequality between the
two radiations and signal will be produced.

20. THE RECORDER
•The amplified signal is used to move an attenuator which cuts
down the radiation coming out of the reference beam until
energy balance is restored.
•This is achieved by a motor which drives the comb into the
reference beam when an absorbing band is encountered and
out of the beam when the band is passed over.
•The recorder pen is also coupled to this motor so that the
comb movement is followed exactly y the pen