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1
Fundamentalsofinfrared
spectroscopy(FT-IR)
KamillaMalek,EmiliaStaniszewska-Ślęzak,KamilaKochan,KatarzynaMajzner
Theinteractionofmatterwithelectromagneticradiationisfundamentalinoptical
spectroscopyanditreliesonabsorption,emissionandscatteringoflightphotons.
Duetosuchinteractionsoneregistersaspectrumconsistingofbandsofagiven
frequency,shapeandintensity.AsthetitleofthisChapterindicatesinfrared
absorptionspectroscopyresultsfromabsorptionoflightquantumfromIRregion,
whichmatchestoenergydiferencebetweenvibrationallevels.TheIRspectrumis
usuallypresentedinascaleofwavenumbers[cm
-1
]andcanbecollectedinthree
regionsofIRradiation.ItshouldbeemphasizedthatIRandRamantechniques
(describedinChapter2)arecomplementarytoeachother,asbothrelayonregi-
strationoftransitionsbetweenvibrationallevels,butinformationthattheypro-
videiscomplementarytoeachother.Thiscanbeillustratedbytheruleofmutual
exclusion,whichstates,thatifamoleculehasacenterofsymmetry,vibration
activeininfraredabsorptionspectrumisinactiveinRamanandviceversa.Themost
frequentlyusedIRregionismid-infraredradiation(MIR,MidInfraRed),which
coverstheregionof400-4000cm-1.WithinthisIRspectrum,aregionfrom400
to1500cm
-1
,called“fingerprint”,isspecificforeachchemicalspeciesandthis
factstrictlyresultsfromcharacteristicsofvibrationalmotiondescribedbynormal
modes.Aregionoffarinfraredradiation(FIR,FarInfraRed,50-400cm
-1
)also
registersnormalmodeswhilearegionabove4000cm-1(NIR,NearInfraRed)pro-
videsinformationaboutovertonesandcombinationmodes.TheabbreviationFT
inthenameofthetechniquemeansFouriertransform-themathematicaloperation
thatdecomposesafunctionoftime(asignal)intothefunctionoffrequency.FT-IR
spectroscopyisappliedfortheidentificationandquantitativeanalysisofchemical
compoundsortheirmixturesaswellasthedeterminationofphysicochemicalfea-
turessuchasmolecularstructureanditschangesduetoastress/reaction,kine-
ticsofreactionsandintramoleculardynamics.IRspectraofasampleinanystate
canbecollected.