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“Introduction To
a

iSR pectroscopy”
ANUM ASLAM

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a

NT

INTRODUCTION.

Absorption Emission

spectroscop spectroscop

UV
spectroscopy Fluorimetry

IR Flame
spectroscop photometery

N MR
spectroscopy

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~ INFRARED SPECTROSCOPY
(IR

spectroscopy) is muaeiine
the spectroscopy that deals Ta an m
with the infrared region of
the electromagnetic ,
SJ ol-f(deU iaa Pm iarcimicm (ela mual aml |
longer wavelength and
t a
e frequency than visible a am

wD rr ri

AUER eetreccc ah ae ee

interacting with a mol ,
hada Aili eReaeleae a a oe a oe 1 |

e It is based on absorption ee
spectroscopy

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ees

IAIED Si =p wos eral.
iia ARED REGIO pe

inate a infrared

 

‘Main infrared region 25-15 (4000-667cm- |
Far infrared region – 15-200 m —(667-100 cm-1)

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——_ <=

PRINCIPLE

e When infrared ‘light’ or radiation hits a molecule, the
bonds in the molecule absorb the energy of the infrared
and respond by vibrating.

= stretch Asymmetric stretch Scissoring

 

rT} 7.
radiation t

vanllin ck Wagging Twisting

Molecular vibrations

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ats 40 $.0 60 70 80 90 10 12 15 20n. Wavelength
= 10° meter

aa | yn *
|

|

| |

– Note inverted peaks
i Top: 100% transmission
bey Bottom: No transmission
4
t Ox UH
£ |

Cc

F: |

| OCH;

OH

vanillin
(CCl, solution)

0
4000 3000 2000 wwwww. .DdulooMMixc.coomm 1000

‘wavenu mbe¢rm

 

 

 

“Molecular Vibrations”

ANTS te weV TVo t

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MOLECULAR
VIBRATIONS

=
L

Fundament Non-
al f

Vibrations

r : .

Stretchin Bending
/ g | : :

Vibration Vibration
i ; L ul

undamental
Vibrations

Over Tones,

Combination
Tones,

 

; L
Fermi

Resonance
Symmetri Asymmetri in-plane Out Of Plane

Cc Cc Bending Bending
]

SS ul L

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a <n —

– —

_

“MOLECULAR VIBRATIONS”

“Any change in shape of the molecule- stretching of
bonds, bending of bonds, or internal rotation around

single bonds’.

Because whenever the interaction b/w
electromagnetic waves & matter occur so change

appears in these vibrations.

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¢ Vibrations which appear as
FUNDAMENTAL band in the spectr. ad.
VIBRATIONS

¢ Vibrations which appears as a
NON. result of fundamental vib.

FUNDAMENTAL
VIBRATIONS

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a

FUNDAMENTAL VIBRATIONS

Fundamental! vibration is also divided into types:

1.Streching
vibration Involves a 1.Bending
continuous change vibrations are
in the inter atomic characterized by a
distance along the change in the angle
axis of the bond b/w two bonds.
b/w 2 atoms. 2.lt requires less
2.It requires more energy so appear
energy so appear at longer
at shorter wavelength.
wavelength.

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——_ — = —_

Now, streching vibration is further divided into :

SYMMETRIC VIB.

¢ Inter atomic distance ¢ Inter atomic distance
b/w 2 atoms b/w 2 atoms Is
increases/decreases. alternate/opposite.

Asymmetric
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nan ari ————————————

Bending vibration is divided into:

IN PLANE . lf all the atoms are
BENDING onsame plane.

¢ /f2 atoms are on
OUT OF same plane while
PLANE the 1 atom is on

BENDING _ opposite plane.

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ie
——

Out plane bending is further divided into:

* Change in angle TWISTING
b/w the plane of ,

« Change in angle
a group of atom b/w the plane of

2 groups of
atoms.

Bending vibrations
Near Near

@ 9 Q@ 9 «3

/

In-plane rocking In-plane scissoring Out-of plane wagging Out-of-plane twisting

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COMBINATION
TONES:

Weak bands that
appear

occasionally at
frequencies that

OVER TONES: are sum/difference
These are of 2 or more

observed at fundamental

twice the bands.

frequency of
strong band.

Ex:

carbonyl group.

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ee ,

—_s e
e

COUPLED INTERACTIONS

Interactions between vibrations can occur
(Coupling) if the vibrating bonds are joined to a
single, central atom.
This is because there is mechanical coupling
interaction between the oscillators.
Example:

C=O (both symmetric and asymmetric stretching
vibrations)

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* The vibrations must be of the same
symmetry species if interaction is to
occur

* Strong coupling of stretching vibrations
o
ccurs when there isacommon atom
between the two vibrating bonds.

SF
* Coupling of bending vibrations occur

s
when there isa common bond between
v
ibrating groups.

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– Coupling is greatest when the coupled groups have
approximately equal energies

– Coupling between a stretching vibration and a bending
vibration occurs if the stretching bond is one side of
an angle varied by bending vibration.

– No coupling is seen between groups separated by two
or more bonds

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Greater
coupling

XeTn

a no

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FACTORS AFFECTING THE FREQUENCY

«Relative mass of the atom
«Force constant of the bonds

«Geometry of the atom

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THE RELATIVE MASS OF THE
ATOMS: heavier the atoms

lower is the vibration frequency
of the bond between them.

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Stronger bonds O-H, N-H & C-H
weaker bonds C-C & C-O bond.

EFFECFTS EOOFF/- C BTBOONNISDD SS:: c- C stre
IS t
c
e hi
x n
p g
e
cted to absorb at a highe

f r
r
equency than C-C stretching.

Example: C=

C 2200emt
C=C 1650cmr’
C-C 1200em

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DegOrf Fereeedom ’

aerate S713

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For non linear molecule 3 degree of freedom represent rotatio
t n
r a
a l
n
sa &
tional motion

For non linear (3n-6)degree of freedom re present fundamen
v t
i a
b l
ra
tions

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All vibrational changes don’t appear as
band

Only those vibrational] changes
c t
h h
a a
n t
ge re
su

i l
n t

di in
p
ole movement appear as band

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HOOKES LAW
e It gives the relation between frequency of oscillation ,
atomic mass , force constant of the bond .

e Thus vibrational frequency is

= 4 mc V£/(MxMy)/(Mx+My)

e C = velocity of light
e F = force constant
e Mx= mass of atom x
e My = mass of atom y

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e Since force constant measures the strength of bond,
value of f is

/ FOR SINGLE – 5×10° dynes/cm
BOND

“FOR SDOONUDB LE’. 700xx1100 ? dynes /cm

FORTRIPLE). 15×10° dynes/cm

BOND

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4
‘Hydrogen Bonding”

FARAH ALI KHAN

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F EFFECT OF HYDROGEN BONDING ON
IR

Ps Donor Group (S-Orbital )

al
Proton Acceptor Group (P-Orbital)

Hydrogen Bonding

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EXAMPLES OF PROTON DONOR AND

PROTON ACCEPTOR GROUP

Carboxyl, Hydroxyl, Amine Or Amide Group

Oxygen, Nitrogen, Halogens And Unsaturated Group

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— een (mel dal = —— —— a f->—. Fl a
i : ” a Fi i. die

=. —— > Ps eS — |
— — —

. V —
a 4 — – __ – — ray ~ a ey J

— A
| a 4 —d

1-Intermolecular Hydrogen Bonding
2-Intramolecular Hydrogen Bonding

 

imntermolec tu!
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ee ——

a ae —— a

ee es a — oa —— ke — _ a el – a

es
aoe! Semel oy — — — py ——

Jt ieee a a – = a — – os —_ ae — – _—

—_ — _— _

— i”

PA
— -_ ——s —

P-Hydroxyacetophenone o-Hydroxyacetophenone

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Stretching bands move towards longer wavelength or
lower frequencies And Bending vibrations shift
CS Se Le lta d TS

Bending vibrations Stretching vibrations

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—_————

 

FACTORS AFFECTING ON
HYDROGEN BONDING

Ma eaeel ta

¥ Concentration
Ae} [-lolb elm Cielo) enl-1 ig

Mae licwaleeliiyg
v Basicity

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USOP MTSE SVET O]
The main parts of IR spectrometer are as follows:

e radiation source

e sample cells and sampling of substances

e monochromators

e detectors
e recorder

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INFRARED SOURCES

IR instruments require a source of radiant energy
which emit IR radiation which must be:

Suffi cient .
intensity » ad aa
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sources of IR radiations are as follows:

GLOBAR:

“7 H Produce
o e
d a
of t

s ed up to
carbi i

d leic on 1300 degre r
e a
diant

centigrade energy from
1-40 mieron

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e NERNST GLOWER:

Rod of Heated up to
Zirconium 1500 degree

and yittrium centigrade

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The spectrum of a gas can be obtained by
permitting the sample to expand into an
evacuated cell, also called a cuvette.

Infrared solution cells consists of two windows
of pressed salt sealed. Samples that are liquid
at
room temperature are usually analyzed in pure
form or in solution. The most common solvents
elas,
Carbon Tetrachloride (CCI4) and Carbon
Disulfide
(CS2).

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Solids reduced to small particles (less than 2 micron) can
be examined as a thin paste or mull. The mull is formed by
grinding a 2-5 milligrams of the sample in the presence of
one or two drops of a hydrocarbon oil (nujol oil). The
resulting mull is then examined as a film between flat salt
e)Felicise

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MONOCHROMATORS

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An infrared detector is a detector that
reacts to infrared (IR) radiation.
lt is simply a transducer of radiant

infrared radiations

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TYP ES OF D I

/

Thermal Non-thermal

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_— ee

TH ERM AL DE T
| Thermal detectors can be used over a

wide range of wavelengths and they
operate at room temperature.

slow | response time and lower
‘ s
e e
l n
at s
i i
v v
e jvi t

to other types of detectors. z

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TYPES OF THERIVIAL DETECTOR

There are four types of thermal detector.

> Bolometers
> Thermocouple and thermopile

ee ma AON =) (16110(o me (=)(-1(60)1 4
> Golay cell

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Bolometer is derived from a Greek word
(bolometron)

Bolo = for something thrown
Metron = measure

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e Abolometer consists of an absorptive element, such
as a thin layer of metal.

e Most bolometers use semiconductor or
superconductor absorptive elements rather than
metals.

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caer

= – aa

Working

Thin layer of
Leste eho

metal Any radiation on the
connected to a absorptive element The temperature

raises its
reservoir temperature above change can be Thermal Mass

that of the reservoir. measured directly Heat Capacity C

with an attached Temparature T

thermometer.

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py THERMOGOURLE AND= =

a THERMOPILE

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.

Temperature changes —: Potential difference
changes

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4 >
Thermopile detectors are voltage-generating
devices, which can be thought of as
miniature arrays of thermocouple junctions.

a 4

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oe a

~ M –
_ es 4 – ut

eee Ae (SMOAICUIASMN list
of 2 pyro electric Rear

AATcUUclArclMESLU lamers :
triglycerine sulphate.

* Pyro electric Infrared
Detectors (PIR)
convert the changes In
incoming infrared light
to electric signals.

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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

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GOLAY CELL

Mey tle elm A elelaye
e Flexible silvered diaphragm

e Whole eel Is fe) with xenon gas.

IR absorber , optical read-coust
systern

compernsation teak

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see

an,
:

Metal cylinder and flexible diaphragm

Temperature increases
Gas is expended and diaphragm deforms

detect as a signal

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Non conducting
Thin film overlaps Absorption of IR valence e- to higher

over non- radiation energy conducting
conducting surface state

Voltage drops e Electrical resistance
decreases

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P7 H: O=.T OV-_ OL_T . AH IC ni! D AE™ T; E=C~. TOR—_

Infrared radiations

Radiation ‘ e— insulating
Photovoltaic detector

| | i pty
Generates a small voltage

Detected as a signal

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&
‘Single/Double Beam
nt Absorption WV elTea kyo ote a

UROOBA IQBAL

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IaiRt ABSORPTI ONN
SPECTROPHOTOIVIETERS

e Asingle beam of light , e Asingle beam of light splits
which can pass through one into two separate beams.
solution at a time (sample or One passes through the
reference). sample, another passes

through the reference.

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SINGLE BEAT
SPECTROPHOTOMETER

Sadri rateieo n Sample Cell

Mono-
Detector

chromator

a —

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IR source

Interferometer

IR Movable

ransducer mirror

 

> Laser

Fixed ee | , detecto

Mirror

Beamsplitter

Mirrors with

center hole /
for laser beam

Sample

compartment

© 2007 Thomson Higher Education

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—_

Te a E
SPECTROPHOTOMETER

Synchronous
Attenuator caniites

Synchronous
Monochromator pale

Attenuator &
Detector panicle

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IR source

(er
ev

Movable

mirror

rixed

mirror)
Sample

compartment Beamsplitter

Ik
transducer

her ECoucation

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-—<—=<——=— — — — — me ee

— ee ee ee ee eee ee eee ee ee

 

“seal cam — ‘mle ie ol oe Wi Sc ee aS cee
33 7 A ~ a / —Z —_ ee ij

— — — }- —_ —

Pr, 4a ee “ales sell alll a me
-s .., 4 = at *

e All frequencies
are examined
simultaneously
in Fourier
Mel oats
infrared (FTIR)
spectroscopy.

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“Applications Of

IR Absorption Spectrocopy”

RABIA KHALID NADEEM

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Since different molecules
with different combination

of atoms produce their
unique spectra, infrared

spectroscopy can be used
to qualitatively identify

substances.

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QUALITATIVE ANALYSIS

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FUNDAMENTAL REGION (ROCK
SALT REGION)

e consisting of the absorption /R spectra is called

bands of the functional “fingerprints” because no

groups. other chemical species will
have similar IR spectrum.

e frequency = 4000-1300cm-!
Single bonds give their

e wavelength = 2.5-8
absorption bands in this
region.
Frequency=1300-650cm- 1

Wavelength=8-15.4

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Wavenumriber, cm™’
5000 4000 3000 2500 2000 1500 1400 1 340 1200 1100 1000~=—- 900

erry TTT TT ] ’ rseas

TC err
100

90
v

: RO
70

5 60
: SO
s

40 CH,CHCH,CH,
S
» 30 C-—H
e
a 20 oe stretch

10}
nN

CH,

J

+ Group frequency region Fingerprint region —

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APPLICATION OF IR SPECTROSCOPOY
TO ORGANIC MOLECULES:

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

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a a d EGIONS OF IR SP E CTRUM:

¢ 4000 and 1300 cm-!
¢ Alcohols and amines

¢ 1300 and 909 cm-!
¢ Complex interactions

¢ 909 and 650 cm-!
¢« Benzene rings

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— STUDYING PROGR ES
REACTIONS

e Observing rate of disappearance of characteristic
absorption band in reactants; or

e Rate of increasing absorption bands in products of a
particular product.

od O—H = 3600-3650 cm-’

C=O = 1680-1760 cm-!

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