detailed study of IR spectroscopy with instrumentation

2. Analytical methods are defined as the set of techniques
that allow us to know qualitatively and / or quantitatively
the composition of any material and identification of the
material
There are a wide variety of techniques used for analysis,
from simple titrations to very advanced techniques using
highly specialized instrumentation.

3. Titrimetric or volumetric methods, Gravimetric methods,
Gasometric analysis.
Instrumental
Analysis
Potentiometry, Conductometry, Polarography,
Amperometric titrations, Refractometry,
polarimetry, Nephelometry & Turbidimetry
Chromatographic paper Chromatography, Thin layer
Chromatography ,column Chromatography,
Gas Chromatography, High pressure liquid
Chromatography
Spectroscopy Ultraviolet –visible spectroscopy, Flourimetry,
Atomic Absorption, spectroscopy ,Infrared
spectroscopy, Nuclear magnetic Resonance
spectroscopy, Mass spectroscopy
Chemical Analysis

6. Absorption
spectroscopy
UV
spectroscopy
IR
spectroscopy
NMR
spectroscopy
Emission
spectroscopy
Fluorimetry
Flame
photometry
Spectroscopy

7.  Infrared spectroscopy (IR
spectroscopy) is
the spectroscopy that deals
with the infrared region of
the electromagnetic
spectrum, that is light with a
longer wavelength and
lower frequency than visible
light
 Infrared Spectroscopy is the
analysis of infrared light
interacting with a molecule.
 It is based on absorption
spectroscopy

8. • IR spectroscopy is concerned with the study of
absorption of infrared radiation, which causes
vibrational transition in the molecule. Hence, IR
spectroscopy also known as Vibrational spectroscopy.
• IR spectra mainly used in structure elucidation to
determine the functional groups.

10. INFRARED REGIONS RANGE
Near infrared region 0.8-2.5 μ(12,500-4000 cm-1)
Main infrared region 2.5-15 μ(4000-667cm-1)
Far infrared region 15-200 m μ(667-100 cm-1)

11. 1. Correct wavelength of radiation
2. Change in dipole moment
1. Correct wavelength of radiation:
A molecule to absorb IR radiation, the natural
frequency of vibrations of some part of a molecule is
the same as the frequency of incident radiation.

12. • A molecule can only absorb IR radiation when its
absorption cause a change in its electric dipole
• A molecule is said to have an electric dipole when there
is a slight positive and a slight negative charge on its
component of atoms.

15. What is a vibration in a molecule?
“Any change in shape of the molecule- stretching of
bonds, bending of bonds, or internal rotation around
single bonds”.
Why we study the molecular vibration?
Because whenever the interaction b/w
electromagnetic waves & matter occur so change
appears in these vibrations.

16. Mol. vibration divided into 2 main Types:
FUNDAMENTAL
VIBRATION
• Vibrations which appear as
band in the spectra.
NON-
FUNDAMENTAL
VIBRATION
• Vibrations which appears as
a result of fundamental vib.

17. Fundamental vibration is also divided into types:
STRETCHING
VIB.
BENDING
VIB.
1.Streching
vibration Involves a
continuous change
in the inter atomic
distance along the
axis of the bond
b/w 2 atoms.
2.It requires more
energy so appear
at shorter
wavelength.
1.Bending
vibrations are
characterized by a
change in the angle
b/w two bonds.
2.It requires less
energy so appear
at longer
wavelength.

18. Now stretching vibration is further divided into:
SYMMETRIC VIB.
• Inter atomic distance
b/w 2 atoms
increases/decreases.
ASYMMETRIC VIB.
• Inter atomic distance
b/w 2 atoms is
alternate/opposite.

21. Bending vibration is further divided into:
• If all the atoms are on
same plane.IN PLANE
BENDING
• If 2 atoms are on same
plane while the 1 atom
is on opposite plane.
OUT OF
PLANE
BENDING

22. In-plane bending further divided into:
SCISSORING:
When 2 atoms
move away or
close towards
each other.
ROCKING:
Change in angle
b/w a group of
atoms.

24.  Out plane bending is further divided into:
• Change in angle
b/w the plane of
a group of atom
WAGGING
• Change in angle
b/w the plane of
2 groups of
atoms.
TWISTING

26. Non-fundamental vibrations
NON-
FUNDAMENTAL
OVER TONES:
These are
observed at
twice the
frequency of
strong band.
Ex:
carbonyl group.
COMBINATION
TONES:
Weak bands that
appear
occasionally at
frequencies that
are sum/difference
of 2 or more
fundamental
bands.
FERMI
RESONANCE:
Interaction b/w
fundamental
vibration &
overtones or
combination
tones.
Ex:CO2

27. When infrared 'light' or radiation hits a molecule, the
bonds in the molecule absorb the energy of the infrared
and respond by vibrating.
IR RADIATION
VANLLINE
MOLECULAR VIBRATIONS

29.  It gives the relation between frequency of oscillation
,atomic mass , force constant of the bond .
 Thus vibrational frequency is
= ½𝛱C√f/(MxMy)/(Mx+My)
 C = velocity of light
 F = force constant
 Mx= mass of atom x
 My = mass of atom y

30.  Since force constant measures the strength of
bond, value of f is
• 5×10⁵ dynes/cmFOR SINGLE
BOND
• 10×10⁵ dynes /cmFOR DOUBLE
BOND
• 15×10⁵ dynes/cmFOR TRIPLE
BOND

31. BOND STRENGTH
ATOMIC MASS

33. The main parts of IR spectrometer are as
follows:
 radiation source
 sample cells and sampling of substances
 monochromators
 detectors
 recorder

36.  IR instruments require a source of radiant
energy which emit IR radiation which must
be:
Sufficient
intensity
Continuous
Stable

37.  Sources of IR radiations are as follows:
GLOBAR:
Rod of silicon
carbide
Heated up to
1300 degree
centigrade
Produce
radiant
energy from
1-40 micron

38. Rod of
zirconium and
yittrium
Heated up to
1500 degree
centigrade
Emits radiation
between 0.4-
20 micron.

39.  Almost invariably in all dispersive instruments, the
sample compartment is positioned before the
monochromator to conserve weak IR energy and
reduce stray radiation and optical aberrations.

40. SAMPLE PREPARATION TECHNIQUES
SOLIDS
Generally 4 techniques are employed for preparing solid
samples:
1. Solids run in solution.
2. Solid Films.
3. Mull technique.
4. Pressed pellet technique

41. • Solids may be dissolved in non-aqueous inert solvent and a
drop of this solution is placed on an alkali metal disc and
solvent is allowed to evaporate, leaving a thin film of solute
(or the entire solution is placed in a liquid sample cell)
which is then mounted in spectrometer.
• If the solution of solid can be prepared in a suitable solvent
then the solution is run in concentration of cells for liquids.
• Some solvents used are chloroform, carbon tetrachloride,
acetone, Cyclohexane etc

42. Demerit:
• This method can’t be used for all solids because suitable
solvents are limited in number & there is no single
solvent
which is transparent throughout IR region.
Precautions:
• Solute chemical interaction with the solvent must be
taken
into consideration especially for compounds having
property
of H-bonding.
• The solvent should not absorb in the studied range.

43. Solid films:
• If a solid is polymer resins & amorphous solids, the
sample is dissolved in any reasonable volatile solvent
& this solution is poured on a rock salt plate (Nacl or
KBr) & solvent is evaporated by gentle heating.
• If solid is non-crystalline, a thin homogenous film is
deposited on the plate which can be mounted and
scanned directly.
• Sometimes polymers can be “hot pressed” onto
plates.

44. Merit and Demerit:
This method is useful for rapid qualitative analysis but
becomes useless for carrying out quantitative analysis

45. Mull technique:
• In this technique a small quantity of sample is thoroughly
ground in a clean mortar until the powder is very fine.
• After grinding, the mulling agent (mineral oil or Nujol) is
introduced in small quantities just sufficient to take up the
powder (mixture approximates the consistency of a
toothpaste).
• The mixture is then transferred to the mull plates & the
plates are squeezed together to adjust the thickness of the
sample between IR transmitting windows.
• This is then mounted in a path of IR beam and the
spectrum is run.

46. Demerit:
• Although Nujol is transparent throughout IR region, yet it
has a disadvantage that it has absorption maxima at 2915,
1462, 1376 & 719 cm-1.
• So when IR spectrum of solid sample is taken in Nujol mull,
absorption bands of solid sample that happen to coincide
with the absorption bands of the Nujol mull will be hidden
(but others will be clearly seen in IR spectrum) and then
interferes with the absorption of the sample.
• This method is good for qualitative analysis but not for
quantitative analysis

47. Pressed pellet technique:
• In this technique a small amount of finely ground solid
sample is intimately mixed with about 100 times its weight
of powdered Potassium bromide, in a vibrating ball mill.
• This finely ground mixture is then pressed under very high
pressure (25000 p sig) in evacuable die or minipress to form
a small pellet (about 1-2 mm thick and 1cm in diameter).
• The resulting pellet is transparent to IR radiation and is
run
as such.

48. • The powder (KBr + sample) is introduced in
between the 2 bolts and the upper screw A is
tightened until the powder is
compressed to a thin disc.
• After compressing the sample bolts A & A1
are removed and a steel cylinder with pellet
inside it is placed in path of the beam of IR
spectrometer and a blank KBr pellet of identical
thickness is kept in the path of reference beam

50. Advantages of this technique over mull technique
• The use of KBr eliminates the problem of bands which
appear in IR spectrum due to the mulling agent as in this
case no such bands appear.
• KBr pellets can be stored for longer periods of time.
• As concentration of the sample can be suitably adjusted
in
pellets, it can be used for quantitative analysis.
• The resolution of spectrum in KBr is superior to that
obtained with mulls

51. Demerits:
• It always has a band at 3450 cm-1, from –OH group of
moisture present in the sample.
• The high pressure involved during the formation of pellets
may bring about polymorphic changes in crystallinity in the
samples, (Especially inorganic complexes) which may cause
complications in IR spectrum. In some cases, even
substitution of the ligand by bromide may be possible in
inorganic complexes.
• This method is not successful for some polymers which are
difficult to grind with KBr.

52. Sampling for liquids:
Liquid samples taken.
•Put it into rectangular cells of KBr, NaCl etc.
•IR spectra obtained.
•For double beam, matched cells are generally employed
•One cell contains sample while other has solvent used in
sample.
•Matched cells should be of same thickness, protect from
moisture.

53. Sampling for gases:
Gases, or liquids with low boiling points, allowed to
expand into an evacuated sample cell gas have Small size
particles hence the cells are large.
•the tube is 10 cm to 1m long
•Multiple reflections can be used to make the effective
path length as long as 40 cm
•Lacks sensitivity

54. A monochromator is a means of separating wavelengths
of the source radiation. The monochromator is used to
separate polychromatic radiation into a suitable
monochromatic form [105]. This is achieved by means of
prisms or diffraction grating. Materials for prism
construction, which are found most suiTable in the
infrared region, are listed in the following Table.

55. Material Optimum ranges of prisms
Glass (Si02) 300 rnp. To 4t (5000 cm-1)
Quartz 800 nv. to 3p, (12500 to 3300 cm-1)
Lithium fluoride 600 mll to 6.1 (1670 cm-1)
Calcium fluoride 200 miA to 9p, (1100 cm-1)
Sodium chloride (NaCI) 200 rniA to 14.511 (625 cm-1)
Potassium bromide (KBr) 10 to 2512 (400 cm-1)
Cesium iodide (CsI) 10 to 344(260 cm-1)

56. An ideal prism instrument would contain large number of
prisms made from different optical materials, so that each
could be used in sequence in its effective region. High
resolution prism instruments contain combination of
Si02, NaCI and KBr prisms. Low-cost instruments use a
NaCI prism over the full range. They give highest
resolution in the vital finger — print region.

57.  A monochromator thus carries out three functions: (i) it
disperses the radiation according to its wave number
components (ii) it restricts the radiation falling on the
detector into a narrow wave number range, and (iii) it
maintains the energy incident on the detector to an
approximately constant level when no sample is present
throughout the wave number range of the instrument

58. Some instruments use a double monochromator. That is,
the exit slit of the first monochromator serves as the
entrance slit for the second monochromator. As a result,
the spectra obtained with spectrophotometers having
double monochromator have higher resolution.

61. Detector
Thermal Non-thermal

63. There are four type of thermal detector
Bolometers
Thermocouple and thermopile
Pyro electric detector
Golay cell

64. Bolometer is derived from a Greek word
(bolometron)
Bolo = for something thrown
Metron = measure

65.  A bolometer consists of an absorptive element,
such as a thin layer of metal.
 Most bolometers use semiconductor or
superconductor absorptive elements rather
than metals.

66. Thin layer of
metal
connected to a
reservoir
Any radiation on
the absorptive
element raises
its temperature
above that of
the reservoir.
The temperature
change can be
measured
directly with an
attached
thermometer.

67. Thermocouples consist of a pair of junctions of
different metals; for example, two pieces of
bismuth fused to either end of a piece of
antimony.

68. Temperature
changes
Potential
difference changes

69. Thermopile detectors are voltage-generating
devices, which can be thought of as a
miniature arrays of thermocouple junctions.

70. Construction:
 Single crystalline
wafer of a pyro
electric material, such
as triglycerine
sulphate.
 Pyro electric Infrared
Detectors (PIR)
convert the changes in
incoming infrared light
to electric signals.

71. Below curie temperature
Pyro electric materials exhibit electrical polarization.
Temperature is altered, the polarization changes.
Observed as an electrical signal(if electrodes are
placed on opposite faces of a thin slice of the
material to form a capacitor)

72. Construction:
 Small metal cylinder
 Flexible silvered diaphragm
 Whole chamber is filled with xenon gas.

73. Metal cylinder and flexible diaphragm
Temperature increases
Gas is expended and diaphragm deforms
detect as a signal

74. Thin film overlaps
over non-
conducting surface
Absorption of IR
radiation
Non conducting
valence e- to
higher energy
conducting state
Electrical
resistance
decreases
Voltage drops

75. Infrared radiations
Photovoltaic detector
Generates a small voltage
Detected as a signal

80. Since different molecules with different
combination of atoms produce their
unique spectra, infrared spectroscopy
can be used to qualitatively identify
substances.

81. QUALITATIVE ANALYSIS

82. Fingerprint Region
 IR spectra is called “fingerprints” because no
other chemical species will have similar IR
spectrum.
 Single bonds give their absorption bands in
this region.
 Frequency=1300-650cm-1
 Wavelength=8-15.4

83. Organic groups differ from one another both in
the strength of the bond and the masses of the
atom involved.

84. • 4000 and 1300 cm-¹
• Alcohols and amines
• 1300 and 909 cm-¹
• Complex interactions
• 909 and 65o cm-¹
• Benzene rings

85.  Observing rate of disappearance of
characteristic absorption band in reactants;
or
 Rate of increasing absorption bands in products
of a particular product.
 E.g.: O—H = 3600-3650 cm-¹
C=O = 1680-1760 cm-¹

86. HOPE YOU
UNDERSTAND MY
PRESENTATION
THANK YOU