《拉曼光譜分析法》

拉曼光譜分析法劉和文1編輯課件RemoteRamanAnalysis

onPlanetaryMissionsToallowRamanspectroscopyatrangeof10'sofmeters.ThisNASA-fundedprojectisaimedatMarslandersorlandersonotherplanets,butalsohasterrestrialuses.2編輯課件激光拉曼光譜根本原理Rayleigh散射：彈性碰撞；無能量交換，僅改變方向；Raman散射：非彈性碰撞；方向改變且有能量交換；Rayleigh散射Raman散射E0基態(tài)，E1振動激發(fā)態(tài)；E0+h0，E1+h0激發(fā)虛態(tài)；獲得能量后，躍遷到激發(fā)虛態(tài).〔1928年印度物理學(xué)家RamanCV發(fā)現(xiàn)；1960年快速開展〕

h

E0E1V=1V=0h

0h

0h

0h

0+

E1+h

0E0+h

0h(

0-

)激發(fā)虛態(tài)3編輯課件根本原理1.Raman散射Raman散射的兩種躍遷能量差：

E=h(

0-

)產(chǎn)生stokes線；強；基態(tài)分子多；

E=h(

0+

)產(chǎn)生反stokes線；弱；Raman位移：Raman散射光與入射光頻率差；ANTI-STOKES

0-

RayleighSTOKES

0+

0h(

0+

)E0E1V=1V=0E1+h

0E2+h

0

h

h

0h(

0-

)4編輯課件Rayleigh/RamanTransitionsIRAbsorptions5編輯課件Rayleigh/RamanTransitionsandSpectra6編輯課件Rayleigh/RamanTransitionsandSpectra7編輯課件TheSpectrumAcompleteRamanspectrumconsistsof:?aRayleighscatteredpeak(highintensity,samewavelengthasexcitation)?aseriesofStokes-shiftedpeaks(lowintensity,longerwavelength)?aseriesofanti-Stokesshiftedpeaks(stilllowerintensity,shorterwavelength)?spectrumindependentofexcitationwavelength(488,632.8,or1064nm)SpectrumofCCl4,usinganAr+laserat488nm.8編輯課件RamanSpectroscopyAnotherspectroscopictechniquewhichprobestherovibrationalstructureofmolecules.C.V.Ramandiscoveredin1928;receivedNobelPrizein1931.Canprobegases,liquids,andsolids.Mustusealasersourceforexcitation.Resurgenceinrecentyearsduetothedevelopmentofnewdetectorswithimprovedsensitivity.ShiftbackawayfromFT-RamantodispersiveRamanwithmultichanneldetectorsystems.9編輯課件InfraredandRamanSpectraofBenzeneIRRaman10編輯課件拉曼光譜與紅外光譜分析方法比較11編輯課件SomeRamanAdvantagesHerearesomereasonswhysomeonewouldprefertouseRamanSpectroscopy.?Non-destructivetosamples(minimalsampleprep)?Highertemperaturestudiespossible(don’tcareaboutIRradiation)?Easilyexaminelowwavenumberregion:100cm-1readilyachieved.?Bettermicroscopy;usingvisiblelightsocanfocusmoretightly.?Easysampleprep:waterisanexcellentsolventforRaman.Canprobesamplethroughtransparentcontainers(glassorplasticbag).12編輯課件WatchforFluorescenceSpectrumofanthracene.A:usingAr+laserat514.5nm.B:usingNd:YAGlaserat1064nm.Wanttouseshortwavelengthbecausescatteringdependson4thpoweroffrequency.…BUT…Wanttouselongwavelengthtominimizechanceofinducingfluorescence.13編輯課件紅外活性和拉曼活性振動①紅外活性振動

ⅰ永久偶極矩；極性基團；ⅱ瞬間偶極矩；非對稱分子；紅外活性振動—伴有偶極矩變化的振動可以產(chǎn)生紅外吸收譜帶.②拉曼活性振動

誘導(dǎo)偶極矩=E非極性基團，對稱分子；拉曼活性振動—伴隨有極化率變化的振動。對稱分子：對稱振動→拉曼活性。不對稱振動→紅外活性

Eeer14編輯課件SelectionRuleforRamanScatteringMustbechangeinpolarizabilityNon-PolargroupssuchasC-S,S-S,C=C,CC(triplebond),N=Nandheavyatoms(I,Br,Hg)strongscatterersSymmetricstretchingvibrationsaremuchstrongerscatterersthanasymmetricstretchingvibrations15編輯課件PolarizationEffects16編輯課件對稱中心分子CO2，CS2等，選律不相容。無對稱中心分子〔例如SO2等〕，三種振動既是紅外活性振動，又是拉曼活性振動。選律

1

2

3

4拉曼活性紅外活性紅外活性振動自由度：3N-4=4拉曼光譜—源于極化率變化紅外光譜—源于偶極矩變化17編輯課件PolarizationofCCl4

18編輯課件PolarizationofCHCl3

19編輯課件Raman位移

對不同物質(zhì)：

不同；對同一物質(zhì)：

與入射光頻率無關(guān)；表征分子振-轉(zhuǎn)能級的特征物理量；定性與結(jié)構(gòu)分析的依據(jù)；Raman散射的產(chǎn)生：光電場E中，分子產(chǎn)生誘導(dǎo)偶極距

=E

分子極化率；20編輯課件由拉曼光譜可以獲得有機化合物的各種結(jié)構(gòu)信息：2〕紅外光譜中，由CN，C=S，S-H伸縮振動產(chǎn)生的譜帶一般較弱或強度可變，而在拉曼光譜中那么是強譜帶。3〕環(huán)狀化合物的對稱呼吸振動常常是最強的拉曼譜帶。1〕同種分子的非極性鍵S-S，C=C，N=N，CC產(chǎn)生強拉曼譜帶，隨單鍵雙鍵三鍵譜帶強度增加。拉曼光譜與有機結(jié)構(gòu)21編輯課件4〕在拉曼光譜中，X=Y=Z，C=N=C，O=C=O-這類鍵的對稱伸縮振動是強譜帶，反這類鍵的對稱伸縮振動是弱譜帶。紅外光譜與此相反。5〕C-C伸縮振動在拉曼光譜中是強譜帶。6〕醇和烷烴的拉曼光譜是相似的：I.C-O鍵與C-C鍵的力常數(shù)或鍵的強度沒有很大差異。II.羥基和甲基的質(zhì)量僅相差2單位。III.與C-H和N-H譜帶比較，O-H拉曼譜帶較弱。22編輯課件紅外與拉曼譜圖比照紅外光譜：基團；拉曼光譜：分子骨架測定；23編輯課件紅外與拉曼譜圖比照24編輯課件RamanandInfraredSpectraofH-C≡C-HAsymmetricC-HStretchSymmetricC-HStretchC≡CStretch25編輯課件Vibrationalmodesofmethane(CCl4)Infraredinactive,RamanactivevibrationsInfraredactive,Ramaninactivevibrations314cm-1776cm-1463cm-1219cm-126編輯課件InfraredandRamanSpectrumofCCl4776cm-1314cm-1463cm-1219cm-1InfraredspectrumRamanspectrum27編輯課件2941，2927cm-1

ASCH22854cm-1

SCH21029cm-1〔C-C〕803cm-1環(huán)呼吸

1444，1267cm-1

CH228編輯課件3060cm-1

r-H)1600,1587cm-1

c=c)苯環(huán)1000cm-1環(huán)呼吸787cm-1環(huán)變形1039,1022cm-1單取代29編輯課件RamanSpectroscopyRelativelysimpleandnon-destructivestructureanalysistechniqueofcarbonmaterialsPowerfultoolforthestructuralcharacterizationofdiamondoramorphouscarbonmaterials.DLCDiamond30編輯課件RemoteRamanAnalysis

onPlanetaryMissionsToallowRamanspectroscopyatrangeof10'sofmeters.ThisNASA-fundedprojectisaimedatMarslandersorlandersonotherplanets,butalsohasterrestrialuses.31編輯課件NSOMRamanImagingSpectrumofpotassiumtitanylphosphate.FromHansHallenatNCSU.Squaresare5x5μmsquareofthismaterialdopedwithRb.Anear-fieldscanningmicroscopewasusedandtheRamansignalwasusedtokeythesubstrateresponse.32編輯課件ChemicalMappingFocuslasertosmallspot.TunespectrometertoparticularRamantransitionpeak.Rasterscanthesampleunderthelaserbeam,recordintensitychanges.Resultantmapcorrelateswithsubstance.Acquireanentirespectrumateverypoint,thenchoosethefeaturewithwhichtokeytheimage.MotorizedstagefromRenishawforchemicalmapping.Thisisadrugtablet.Theyellowcorrespondstotheactiveingredient.Particlesareinthe10’sofμmrange.33編輯課件ChemicalImagingNowdefocusthelaser(notasmallspotbutrather“baths〞thesampleinlaserradiation).Passtheemittedradiationthroughanarrowbandpassfilter,adjustedtoaparticularwavelength,chosentobeacertainRamanband.FocusthislightontheCCDcamera.BrightregionscorrespondtolocationsofsubstancegivingrisetoRamansignal.Mixtureofcocaineandsugar.Brightspotsarecocaine.34編輯課件Applications-ArtRestorationThis12centuryfrescoonachurchwallinItalyneededtoberestored.Whatpaintstouse?Ramananalysisclearlyidentifiedthepaintsandpigmentsthatwereoriginallypresent,permittingacorrectchoiceofcleaningmaterialsandsubsequentrepaintingtorestoreitsoriginalcondition.35編輯課件Applications-PaintChipsForensicanalysisofpaintchipsinvehicleaccidents.Oftenmultiplelayers.CananalyzewithIRbystrippingsuccessivelayers.ImageedgewithmicroRaman.Layers1and3turnedouttoberutilephaseTiO2-awhitepaint.Layer2wasaGoethite,aredpigmentandcorrosioninhibitor.Layer4wasmolybdateorange,acommonredpaintinthe70’sinNorthAmericaandstillusedintheU.K.today.Layer5wasasilicatebasedpaint.DataarisingfromacaseinvestigatedbyLAPD.36編輯課件Applications-GemForgeryIn1999anewprocesswasdeveloped–calledGEPOL–wherebybrowntypeIIadiamondscouldbetreatedtobecomeindistinguishablefromnaturallycleardiamonds.Ramanpresentedwaytodistinguishthem.NaturallycleardiamondOriginallybrowndiamond37編輯課件Applications-BulletProofGlassIdentifypoly(carbonate)frompoly(methylmethacrylate).Bothusedforshatter-proofglass38編輯課件Applications-SunscreenFormulationsHerearethespectraof5commonsunscreeningredients.Ramanisabletodeterminefromaspectrumonthearmthenatureofthesunscreenbeingused.A:ODPABA(octylN,N-dimethyl-p-aminobenzoicacid)B:OMC(octylp-methoxycinnamate)C:BZ3(oxybenzone)D:OCS(octylsalicylate)E:DBM(dibenzoylmethane)G.R.Luppnowetal.,J.Raman.Spec.34,743(2003).39編輯課件激光Raman光譜儀

laserRamanspectroscopy激光光源：He-Ne激光器，波長632.8nm；

Ar激光器，波長514.5nm，488.0nm；散射強度1/4單色器：

光柵，多單色器；檢測器：光電倍增管，光子計數(shù)器；40編輯課件傅立葉變換-拉曼光譜儀FT-Ramanspectroscopy光源：Nd-YAG釔鋁石榴石激光器〔1.064m〕；檢測器：高靈敏度的銦鎵砷探頭；特點：〔1〕防止了熒光干擾；〔2〕精度高；〔3〕消除了瑞利譜線；〔4〕測量速度快。41編輯課件SourcesRamanintensityisweakandtheexcitationsourcemustbestrongtogeneratesufficientsignal.Sourcemustbemonochromaticsothatspectrumissufficientlyuncomplicated.Intenselampscanwork,butwhenmonochromatized,haveverylittlepower.Scatteringefficiencyincreasesasn4:thebluerthelight,themorethescattering.Thebluerthelight,thegreaterthechanceofproduci