The preferred method of infrared spectroscopy is known as Fourier Transform InfraRed (FT-IR). Infrared spectroscopy involves passing IR photons through a sample. The sample absorbs some of the infrared light and passes some of it through (transmitted). The resulting spectrum depicts the sample's molecule absorption and transmission, resulting in a molecular fingerprint.

1. Introduction to FTIR By Rahul Verma
Sample Prepration
Instrumentation
Principal of FTIR
Types of Vibration
Introduction
Contents
Introduction of FTIR

2. Introduction to FTIR By Rahul Verma
Chemistry is the
science of study matter
and energy and
interaction between
them.
Chemistry
Matter
Energy
Interaction
Introduction
Chemistry

3. Introduction to FTIR By Rahul Verma
Introduction:
Spectroscopy
Spectroscopy is the science
of study the interaction
between radiation and
matter
Sample
(Matter)
Emission
Spectroscopy
Absorption Emission
A A
hʋ
hʋ
eˉ
eˉ
Electromagnetic
Radiation

4. Introduction to FTIR By Rahul Verma
Introduction
Fourier Transfer Infrared
For both
organic and
inorganic
compounds
Measuring the
absorption of
IR radiation
Information
about chemical
nature and
molecular
structure
Deals with the
interaction of
infrared
radiation with
matter

5. Introduction to FTIR By Rahul Verma
According to Maxwell’s Classical theory
The propagation of electromagnetic
radiation in a vacuum is constant for all
regions of the spectrum.
E
M
D
velocity of light
c =  × 
Wave number
Electromagnetic radiation can be
regarded as a stream of particles or
quanta, for which the energy.
Modification of Einstein, Planck and Bohr
Bohr equation
Electromagnetic spectrum
Introduction

6. Introduction to FTIR By Rahul Verma
Molecular
spectra
Electronic Spectra
(UV-visible-near IR)
Vibrational Spectra
(IR region)
Rotational spectra
(microwave region)
Vibration
Transitions between a
specific vibrational and
rotational level of one
electronic state to another.
Transitions from the rotational
levels of one vibrational level
to the rotational levels of
another vibrational level in
the same electronic state.
Transitions between rotational
levels of the same vibrational
level of the same electronic state

7. Introduction to FTIR By Rahul Verma
Molecular
Vibration
Molecular
Vibration
Rotational
Translation
Vibrations
A molecule has as many degrees of
freedom as the total degree of
freedom of its individual atoms.
Each atom has three degrees of
freedom (corresponding to the
Cartesian coordinates), thus in an
N-atom molecule there will be 3N
degree of freedom.
Q How many vibrations are possible..?
Relative positions of the
atoms change while the
average position and
orientation of the molecule
remain fixed: 3 rotational
freedom (nonlinear), 2
rotational freedom
(linear).
Inter-atomic distances
remain constant but the
entire molecule rotates
with respect to three
mutually perpendicular
axes.
The movement of the
entire molecule while the
positions of the atoms
relative to each other
remain fixed (3 degrees
of translational
freedom).
Degree of Freedom Linear Non- Linear
Translational 3 3
Rotational 2 3
Vibrational 3N-5 3N-6
Total 3N 3N
N= Number of atom in molecule

8. Introduction to FTIR By Rahul Verma
Type
of
Vibration
Type of Vibration
Two different types of vibrational
Stretching mode
Vibrations can either involve a
change in bond length
(stretching) or bond angle
(bending)
Symmetrical
Stretching
Asymmetrical
Stretching
Four different types of bending
vibrational modes
Scissoring, Rocking,
Wagging, and Twisting.
Scissoring Rocking Wagging Twisting

9. Introduction to FTIR By Rahul Verma
Principal
Principal of IR Spectroscopy
1
Molecule are
made up of
atom and linked
by bond.
2
The movement
of atoms and
chemicals bond
like spring and
ball system.
3
The Energy of
molecular
vibration is
Quantized.
4
When EMR
(IR) is applied
then it causes
the vibration
between the
atoms of
molecule.
5
Energy
transferred to
molecule by
resonance when
vibration
frequency is the
same.

10. Introduction to FTIR By Rahul Verma
Principal
Absorption region of IR spectra
IR Spectra
Two
Region
Group
frequencies
region
Fingerprint
region
✓ The region to left-hand side of
diagram (4000-1300 cm-1) .
✓ Vibrational frequencies are
nearly independent of the rest
of the molecule.
✓ Functional or structural
groups.
✓ The region to right-hand side of
diagram (1300-400 cm-1) .
✓ Vibrational frequencies are affected
by the entire molecule, as result
broader ranges for group
absorptions.
✓ Usually contain very complicated
series of absorption.

11. Introduction to FTIR By Rahul Verma
IR Inactive
Principal
Molecule will
absorb IR if the
change in
vibrational states is
associated with a
change in the
dipole moment ()
of the molecule.
Selection
Rule
µ = qr
q: electrical
charge
r: directed
distance
IR Active
Spectra of Carbon Dioxide

12. Introduction to FTIR By Rahul Verma
Principal
IR
Spectra
X- Axis= Wavelength or wavenumber
Y-Axis=
%
T
or
A
ºI
I
T = I/Io
%T = 100*I/Io
A = -log* T
T=transmittance
A=absorbance

13. Introduction to FTIR By Rahul Verma
Principal
IR-
Spectra
Overtone of
1720
C-H
Stretching
2900
C=O Stretching 1720
CH3C=O
Bending
1365
C-CO-C
Bending
1170
Copyright for NIST Standard Reference Data is governed by the standard reference data act.
N-H Stretch
C-H
Stretching
3050
NH2 Scissoring
1621
C-N Stretch
1277
NH2 wagging
700

14. Introduction to FTIR By Rahul Verma
Widely applied and quite
popular in the far-IR
and mid-IR
spectrometry
Instrumentation
Dispersive
instruments
Fourier transform
IR (FTIR)
Add Your Text
with a
monochromatic to
be used in the mid-
IR region for
spectral scanning
and quantitative
analysis.
Non-dispersive
instruments
Widely applied and quite
popular in the far-IR
and mid-IR
spectrometry

15. Introduction to FTIR By Rahul Verma
Dispersive IR spectrophotometers
Modern dispersive IR
spectrophotometers are invariably
double-beam instruments, but many
allow single-beam operation via a
front-panel switch
Double-beam operation allows a
stable 100% T baseline in the
spectra.
Instrumentation

16. Introduction to FTIR By Rahul Verma
Instrumentation
Component
of
IR
spectrophotometers
IR Source
Optical System
Window
Reflection Grating
And Mirror
Detector
Used for sample cells and to permit various compartment to be isolated from the
environment.
Reflection gratings : To reduce the effect of overlapping orders and stray radiation,
filters or a preceding prism are usually employed.
Mirrors: but not lenses are used to focus and collimate the IR radiation. Generally
made from Pyrex or another material with low coefficient of thermal expansion.
Thermocouple thermoelectric effect -
dissimilar metal junction
cheap, slow,
insensitive
Bolometer Ni, Pt resistance thermometer
(thermistor)
Highly sensitive
<400 cm-1
Pyroelectric Tri glycine sulfate piezoelectric
material
fast and sensitive
(mid IR)
Photoconducting PbS, CdS, Pb Se light sensitive
cells
fast and sensitive
(near IR)
The system that works in the infrared band of the optical wave, which is the
optical system that receives or sends infrared light waves.
Nernst Glower heated rare earth oxide rod 1-50 µm (mid- to far-IR)
Globar heated SiC rod (~1500 K) 1-50 µm(mid- to far-IR)
W filament lamp 1100 K 0.78-2.5 µm (Near-IR)
Hg arc lamp plasma 50 - 300 µm (far-IR)
CO2 laser stimulated emission lines 9-11 µm

17. Introduction to FTIR By Rahul Verma
Instrumentation
Fourier Transform Infrared (FTIR)
1
FTIR provides
an alternatives to
the use of
monochromators
based on
dispersion.
2
FTIR generates
time-domain
spectra as the
immediately
available data.
3
In conversional dispersive
spectroscopy, frequencies are
separated and only a small
portion is detected at any
particular instant, while the
remainder is discarded. The
immediate result is a
frequency-domain spectrum
4
Direct observation of a
time-domain spectrum is
not immediately useful
because it is not possible
to deduce, by inspection,
frequency-domain spectra
from the corresponding
time-domain waveform.
Time-domain spectra frequency-domain spectrum

18. Introduction to FTIR By Rahul Verma
Fourier Transform Infrared Spectrometer
Instrumentation
FTIR
Single
Beam
Double
Beam

19. Introduction to FTIR By Rahul Verma
Instrumentation
Concept
of FTIR
Interferometer
If moving mirror moves 1/4 λ (1/2 λ round-
trip) waves are out of phase at beam-
splitting mirror - no signal
If moving mirror moves 1/2 λ (1 λ round-
trip) waves are in phase at beam-splitting
mirror – signal
Interferograms
Michelson interferometer
Difference in path length called retardation 
Plot  vs. signal - cosine wave with frequency proportional to light
frequency but signal varies at much lower frequency
One full cycle when mirror moves distance l/2 (round-trip = l)
Frequency of signal
Substituting =c/ VMM velocity of moving mirror


MM
MM V
V
f
2
2
/
=
=
Bolometer, pyroelectric, photoconducting IR detectors can "see“
changes on 10-4 s time scale!

 10
10
10
/
10
3
/
3 −
=

=
s
cm
s
cm
f

20. Introduction to FTIR By Rahul Verma
Sample
Preparation
Sample Preparation
Infrared spectra may be obtained for gases, liquids or solids
Solid samples
Spectra of solids are obtained as
alkali halide discs (KBr), mulls (e.g.
Nujol, a highly refined mixture of
saturated hydrocarbons) and films
(solvent or melt casting)
Alkali halide discs
A milligram or less of the fine ground
sample mixed with about 100 mg of
dry KBr powder in a mortar or ball
mill. The mixture compressed in a
die to form transparent disc.
Mulls
Grinding a few milligrams of the
powdered sample with a mortar or
with pulverizing equipment. A few
drops of the mineral oil added
(grinding continued to form a
smooth paste).
Liquid samples
Pure or solute in transparent
solvent – not water (attacks
windows)
The sample is most often in the
form of liquid films
(“sandwiched” between two
NaCl plates)
Adjustable path length (0.015 to
1 mm) – by Teflon spacer
Gas samples
A gas sample cell consists of a
cylinder of glass or sometimes
a metal. The cell is closed at
both ends with an appropriate
window materials (NaCl/KBr)
and equipped with valves or
stopcocks for introduction of
the sample.

21. Introduction to FTIR By Rahul Verma
USE
of
FTIR
Determination of molecular structure/geometry. e.g. Determination of bond
lengths, bond angles of gaseous molecules
Qualitative analysis – simple, fast, nondestructive.
The fundamental vibrations of many organometallic and inorganic molecules
fall in this region due to the heavy atoms and weak bonds in these molecules.
Lattice vibrations of crystalline materials occur in this region. Electron
valence/conduction band transition in semiconductors often correspond to far-IR
wavelengths.
Use of FTIR

22. Introduction to FTIR By Rahul Verma
Reproducible
And
inexpensive
High
S/N
ratios
Rapid (<10 s)
and
very high
sensitivity
Very high
resolution (<
0.1 cm –1 )
Advantage
of FTIR
To improve S/N ratio
Usually to improve resolution
decrease slit width but less light
makes spectrum "noisier" - signal to
noise ratio (S/N).
n
N
S
S
S
S
n
N
S
i
=
−
=
 2
)
(
S/N improves with more scans
(noise is random, signal is not!)

23. Introduction to FTIR By Rahul Verma
Reference
J. Workman, A.W. Springsteen, “Applied
Spectroscopy”, Academic Press, 1998.
J.M. Hollas, “Modern Spectroscopy”, John
Wiley&Sons, 1996.
B. Stuart, W.O. George, D.J. Ando, “Modern Infrared
Spectroscopy”, John Wiley&Sons, 1997
B. Schrader, D. Bougeard, “Infrared and Raman Spectroscopy:
Methods and Applications”, John Wiley&Sons, 1995.
Reference