InfraredSpectroscopyTransmissionVsATR红外光谱透射比ATR

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1、InfraredSpectroscopy:ComparisonofTransmissionandATRTechniquesMattHerringLewisUniversityOverviewIRspectroscopytheoryTransmissionvs.AttenuatedTotalReflectance(ATR)techniquesBasedonstudyby:Koulis,Cynthia,et.al.ComparisonofTransmissionandInternalReflectionInfraredSpectraofCocaine.JournalofFo

2、rensicSciences,2001.WhatisSpectroscopy?Spectroscopy-studyoftheinteractionofatomsandmoleculeswithelectromagneticradiationProbetheworldatanatomicandmolecularlevelqualitativeanalysisBondlengthsBondForceConstantsMolecularstructuresquantitativeanalysisQuantumStatesAbsorptionofelectromagneticr

3、adiationexcitationtohigherenergystateshv=

4、E2–E1

5、Electronic>Vibrational>RotationalInfraredRadiationFrequencies-12800to10cm-1(cm-1=wavenumbers)DividedintothreeRegionsNear:12800to4000cm-1Middle:4000to200cm-1Far:200to10cm-1Radiationofmostuseforspectroscopyfallsinthemid-infraredregionbetween

6、4000to670cm-150InfraredAbsorptionAbsorptionofIRradiationexcitationofvibrationalandrotationalenergylevelsnotsufficientenergyforelectronicexcitationVibrationalenergystatesareofgreatestimportanceforIRspectroscopyDynamicDipoleMomentAbsorptionofIRradiationisonlyobservedinmoleculeswithadynami

7、cdipolemomentAninduceddynamicdipolemomentisobservedinpolarmoleculesMagnitudeofdipolemomentdependsonoverlapofelectrondensitiesinmoleculeVibrationresultsinchangeininternucleardistanceandthereforefluctuationsinmagnitudeofdipoleHomonucleardiatomicmolecules(e.g.H2,N2,O2)don’tabsorbIRradiation

8、,b/cofnodynamicdipolemomentIRabsorptionIFvibrationalfrequencyofmolecule=frequencyofradiationTHENenergyisabsorbedResultspromotiontohigherenergylevelandincreaseinamplitudeofmolecularvibrationMolecularVibrationsMolecularVibrationalandBendingmodesSingleabsorptionpeakappearsforeachmodewithady

9、namicdipolemomentInterpretingtheSpectraPeaksareidentifiedby:-Intensity-Shape-PositionCorrelationchartsareusedtoaidinidentifyingfunctionalgroupabsorptionbandsDeterminingpeakpositionUsingthemodelofasimpleharmonicoscillatorthefrequencyvibrationcanbepredictedWavenumber=(2πc)-