仪器分析英文原版教案(4)

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1、InfraredSpectrometry(Chapter16&17)~750-3000nmRegionEnergyWavenumberWavelength(kJ/mol)(cm-1)(µm)NearIR150-5012,800-40000.78-2.5MidIR50-2.54000-2002.5-50FarIR2.5-0.1200-1050-1000EnergyofIRphotoninsufficienttocauseelectronicexcitationbutcancausevibrationalorrotationalexcitationMoleculeelectricfield(

2、dipolemoment)interactswithIRphotonelectricfield(bothdynamic)Magnitudeofdipolemomentdeterminedby(i)charge(ii)separationofchargeVibrationorrotationcausesvaryingseparation+-+-+-CEM333page6.1MoleculemusthavechangeindipolemomentduetovibrationorrotationtoabsorbIRradiationAbsorptioncausesincreaseinvibra

3、tionamplitude/rotationfrequencyMoleculeswithpermanentdipolemoments(µ)areIRactived+d-H-ClO-ONodipolemomentHCl,H2O,NOAtoms,O2,H2,Cl2IRactiveIRinactiveµmeasuredindebye(D)1D=3.33x10-30Cám10Dequivalentto+1and-1chargeseparated1CEM333page6.2TypesofMolecularVibrations:StretchBendchangeinbondlengthchangei

4、nbondanglesymmetricscissoringasymmetricwaggingrockingtwisting/torsionnrsnass+w+--t+CEM333page6.3OnlysomemodesmaybeIRactive:ExampleCO2O=C=Olineard-2d+d-Nonetdipolemomentchanged-2d+d-Netdipolemomentchanged-2d+d-NetdipolemomentchangensnotIRactivenas,bendIRactiveCEM333page6.4Classicalvibrationalmotio

5、n:-yMassDisplacementym+yForcerequiredtodisplacemisF=-k×yHooke'sLawspringconstant(N/m)CEM333page6.5Energyisforce´distancedE=-FdydE=kydyEyTotalEnergyòdE=kòydy0o12E=ky2ParabolicEvs.displacementcurveofharmonicoscillator(Fig16-3)CEM333page6.6Classicalvibrationalfrequency:1knclassical=nindependentofene

6、rgy2pmTwomasses?1km1×m2nclassical=m=reducedmass2pmm1+m2Whataboutquantummechanics?æ1öhkæ1ö(1)E=n+=n+h×nclassicalè2ø2pmè2øVibrationalquantumnumber(0,1,2...)1E0=hnclassicalGroundvibrationalstate(n=0)23E1=hnclassicalFirstexcitedstate(n=1)2DE=hnclassicalCalculatedDEoftenagreesquitewellwithexperimentnc

7、alculated(C=O)=1600cm-1nexperiment(C=O)=1600-1800cm-1Seeexample16-1(2)Dn=±1VibrationalSelectionRuleSincelevelsequallyspaced-shouldseeoneabsorptionfrequencyCEM333page6.7Anharmonicoscillator:Mustmodifyharmonicoscillatorp