FT-IR Characterization Lecture note.pdf

Lecture note

1. Material Characterisation Technique
FTIR Spectroscopy
Presented By: Bhawna Vermani
(Ph.D. in Nanotechnology 2
nd
Year)
NANOTECHNOLOGY (BASICS TO ADVANCED) Batch -III
Guru Jambheshwar University of Science and Technology, Hisar

2. FTIR –Fourier Transform Infrared Spectroscopy
•Infraredabsorptionspectroscopyisthemethodusedtodeterminethestructuresofmolecules
withthemolecule’scharacteristicabsorptionofinfraredradiation.
•AnFTIRspectrometersimultaneouslycollectshigh-resolutionspectraldataoverawidespectral
range.
•1881-MichelsonInterferometer
•1949-FirstFT-IRspectrumwasrecordedbyPeterFellgett
FTIR Instrument by Perkin Elmer

3. Infrared Waves
Infraredradiationisarelativelylowenergylightinthe
electromagneticspectrumwhichhaswavelengthaboveredvisible
lightinrangeof780nmand1mm.

4. Molecular Vibration
•Whenexposedtoinfraredradiation,samplemoleculesselectivelyabsorbradiationofspecific
wavelengthswhichcausesthechangeofdipolemomentofsamplemolecules.
•Consequently,molecularvibrationtakesplacebetweenthebonds.Eachbondrequires
differentfrequencyforabsorption.Hence,characteristicpeakisobservedforevery
functionalgrouporcompositions.
•Theintensityofabsorptionpeaksisrelatedtothechangeofdipolemomentandthe
possibilityofthetransitionofenergylevels.

5. Selection Rule for FTIR
•Dipole moment as a polar bond is usually IR active. The non-polar bond in a symmetrical
molecule will absorb weakly or not at all.
Example: Hydrogen bonds, sulphide bonds, amines, alkaline etc.
•The IR energies correspond to the energies of bond stretching to excite the electrons to the
new quantum level.
Applications of FTIR
•Qualitative Analysis (via wavenumber)
•Quantitative Analysis (via Intensity)

6. Dispersive Spectrometer Vs FTIR
FasterDataCollectionduetosimultaneousanalysisintimedomain
Greatspectralquality
Highdatacollectionspeedasthescantimeofallfrequenciesisshort
Thesignal-to-noiseratioofspectrumissignificantlyhigher
Theaccuracyofwavenumberishigh.Theerroriswithintherangeof±
0.01cm
-1
.

7. Principle of FTIR
•MichelsoninterferometeristhecoreofFTIR
instrumentandisusedtosplitonebeamoflight
intotwosothatthepathsofthetwobeamsare
different.
•Thebeamsplitterisdesignedtotransmithalfofthe
lightandreflecthalfofthelight.Subsequently,the
transmittedlightandthereflectedlightstrikethe
stationarymirrorandthemovablemirror,
respectively.
•Whenreflectedbackbythemirrors,twobeamsof
lightrecombinewitheachotheratthebeamsplitter.
ThentheMichelsoninterferometerrecombinesthe
twoandconductsthemintothedetectorwherethe
differenceoftheintensityofthesetwobeamsare
measuredasafunctionofthedifferenceofthe
paths.
•FourierTransformofthetimesignalconvertsitinto
frequencydomainandrepresentsallthepeaks.
BlockDiagramofFTIR

8. Hooke’s Law and Wavenumber
The frequency wavenumber depends upon the force constant and the reduced mass
with Hooke’s Law which is given as:
??????=
�
�????????????
??????
??????
Where,
??????is wave number (1/λ) 4,000 to 400 cm
-1
k is force constant
??????is reduced mass which is given as average of two mass

9. Hooke’s Law and Wavenumber
•Hydrogen bonds have smaller mass (μ), so they lie on high wavenumber side.
•Bonds with increasing s character, needs high energy to vibrate as force constant
(k) is high, bond strength is high. Therefore, wave number for
Triple Bonds> Double Bonds> Single Bonds
•Fingerprintregionconsistsofallmetallicbondsandhalogenbonds.

10. Methodology
•KBrPelletactsasacarrierasitdoesnotshowanyabsorptionbecauseithas
100%transmittanceintheIRregion(4000-400cm-1)withelectronegativity
of2.0basedonthePaulingscale.
•PotassiumBromide(KBr)PelletformationwithKBr:Sample=1000:1
•Forliquidsamplesandtoavoidtimecumbersomesamplepreparation
techniqueAttenuatedtotalreflection(ATR)modeispreferredinwhichdirect
measurementofsamplesforFTIRisfeasible.
•ATRmethodinvolvespressingthesampleagainstahigh-refractive-index
prismwhichmeasuresthechangesthatoccurinatotallyinternallyreflected
infraredbeamaftergettingincontactwiththesample.

11. FTIR Spectrum
•FourierTransformInfraredSpectroscopy(FTIR)identifies
chemicalbondsinamoleculebyproducinganinfrared
absorptionspectrum.Thespectraproduceaprofileofthe
sample,adistinctivemolecularfingerprintthatcanbeused
toscreenandscansamplesformanydifferentcomponents.
•Thex-axis—orhorizontalaxis—representstheinfrared
spectrum,whichplotstheintensityofinfraredspectra.
•They-axis—orverticalaxis—representstheamountof
infraredlighttransmittedorabsorbedbythesample
materialbeinganalyzed.
•WemakeuseoftheORIGINsoftwaretoanalyzetheFTIR
spectrum.Withthehelpofthisprogramme,weprocessesthe
spectrumandmarkthepeakswiththeirwavenumbersto
distinguishthevariousfunctionalgroups,whichfurther
revealinformationaboutthesample'scomposition.
FTIRSpectrum

12. FTIR Spectrum Analysis
•Accordingtothereactionsandcompositionofthesample,thewavenumbersmaygetshift.However,the
referencewavenumberforsomestandardfunctionalgroupsarebelow:
WAVENUMBER (cm-1) Functional Group
4000-3000 cm
-1
O-H, N-H stretching
3000-2500 cm
-1
C-H, S-H stretching
2400-2000 cm
-1
O=C=O stretching (2349), CΞN, CΞC stretching (2260-2190), N=N=N stretching
(2160-2120), C=C=O (2150), C=C=C stretching (2000-1900), C=C=N stretching
(2000)
2000-1650 cm
-1
C=O stretching (1818), C=N stretching (1690-1640)
1670-1600 cm
-1
C=C stretching (1650-1600), N-H bending (1650-1580)
1600-1300 cm
-1
N-O stretching (1550-1500), C-H bending
1400-1000 cm
-1
O-H bending, S=O stretching, C-F stretching, O-H bending, S=O stretching, C-N
stretching, C-O stretching
1000-650 cm
-1
C=C bending, C-Cl stretching, C-Br stretching, C-I stretching
900-700 cm
-1
C-H bending

13. Thank You