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拉曼光譜分析法 劉和文 RemoteRamanAnalysisonPlanetaryMissions ToallowRamanspectroscopyatrangeof10 sofmeters ThisNASA fundedprojectisaimedatMarslandersorlandersonotherplanets butalsohasterrestrialuses 激光拉曼光譜基本原理 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 h 0 E1 h 0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年快速發(fā)展 基本原理 1 Raman散射Raman散射的兩種躍遷能量差 E h 0 產(chǎn)生stokes線 強(qiáng) 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 Rayleigh RamanTransitions IRAbsorptions Rayleigh RamanTransitionsandSpectra Rayleigh RamanTransitionsandSpectra TheSpectrum AcompleteRamanspectrumconsistsof aRayleighscatteredpeak highintensity samewavelengthasexcitation aseriesofStokes shiftedpeaks lowintensity longerwavelength aseriesofanti Stokesshiftedpeaks stilllowerintensity shorterwavelength spectrumindependentofexcitationwavelength 488 632 8 or1064nm SpectrumofCCl4 usinganAr laserat488nm RamanSpectroscopy Anotherspectroscopictechniquewhichprobestherovibrationalstructureofmolecules C V Ramandiscoveredin1928 receivedNobelPrizein1931 Canprobegases liquids andsolids Mustusealasersourceforexcitation Resurgenceinrecentyearsduetothedevelopmentofnewdetectorswithimprovedsensitivity ShiftbackawayfromFT RamantodispersiveRamanwithmultichanneldetectorsystems InfraredandRamanSpectraofBenzene IR Raman 拉曼光譜與紅外光譜分析方法比較 SomeRamanAdvantages HerearesomereasonswhysomeonewouldprefertouseRamanSpectroscopy Non destructivetosamples minimalsampleprep Highertemperaturestudiespossible don tcareaboutIRradiation Easilyexaminelowwavenumberregion 100cm 1readilyachieved Bettermicroscopy usingvisiblelightsocanfocusmoretightly Easysampleprep waterisanexcellentsolventforRaman Canprobesamplethroughtransparentcontainers glassorplasticbag WatchforFluorescence Spectrumofanthracene A usingAr laserat514 5nm B usingNd YAGlaserat1064nm Wanttouseshortwavelengthbecausescatteringdependson4thpoweroffrequency BUT Wanttouselongwavelengthtominimizechanceofinducingfluorescence 紅外活性和拉曼活性振動 紅外活性振動 永久偶極矩 極性基團(tuán) 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 拉曼活性振動誘導(dǎo)偶極矩 E非極性基團(tuán) 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 SelectionRuleforRamanScattering MustbechangeinpolarizabilityNon PolargroupssuchasC S S S C C C C triplebond N Nandheavyatoms I Br Hg strongscatterersSymmetricstretchingvibrationsaremuchstrongerscatterersthanasymmetricstretchingvibrations PolarizationEffects 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 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 PolarizationofCCl4 PolarizationofCHCl3 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 由拉曼光譜可以獲得有機(jī)化合物的各種結(jié)構(gòu)信息 2 紅外光譜中 由C N C S S H伸縮振動產(chǎn)生的譜帶一般較弱或強(qiáng)度可變 而在拉曼光譜中則是強(qiáng)譜帶 3 環(huán)狀化合物的對稱呼吸振動常常是最強(qiáng)的拉曼譜帶 1 同種分子的非極性鍵S S C C N N C C產(chǎn)生強(qiáng)拉曼譜帶 隨單鍵 雙鍵 三鍵譜帶強(qiáng)度增加 拉曼光譜與有機(jī)結(jié)構(gòu) 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(qiáng)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(qiáng)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(qiáng)度沒有很大差別 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 紅外與拉曼譜圖對比 紅外光譜 基團(tuán) 拉曼光譜 分子骨架測定 紅外與拉曼譜圖對比 RamanandInfraredSpectraofH C C H AsymmetricC HStretch SymmetricC HStretch C CStretch Vibrationalmodesofmethane CCl4 Infraredinactive Ramanactivevibrations Infraredactive Ramaninactivevibrations 314cm 1 776cm 1 463cm 1 219cm 1 InfraredandRamanSpectrumofCCl4 776cm 1 314cm 1 463cm 1 219cm 1 Infraredspectrum Ramanspectrum 2941 2927cm 1 ASCH2 2854cm 1 SCH2 1029cm 1 C C 803cm 1環(huán)呼吸 1444 1267cm 1 CH2 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 RamanSpectroscopy Relativelysimpleandnon destructivestructureanalysistechniqueofcarbonmaterialsPowerfultoolforthestructuralcharacterizationofdiamondoramorphouscarbonmaterials RemoteRamanAnalysisonPlanetaryMissions ToallowRamanspectroscopyatrangeof10 sofmeters ThisNASA fundedprojectisaimedatMarslandersorlandersonotherplanets butalsohasterrestrialuses NSOMRamanImaging Spectrumofpotassiumtitanylphosphate FromHansHallenatNCSU Squaresare5x5 msquareofthismaterialdopedwithRb Anear fieldscanningmicroscopewasusedandtheRamansignalwasusedtokeythesubstrateresponse ChemicalMapping Focuslasertosmallspot TunespectrometertoparticularRamantransitionpeak Rasterscanthesampleunderthelaserbeam recordintensitychanges Resultantmapcorrelateswithsubstance Acquireanentirespectrumateverypoint thenchoosethefeaturewithwhichtokeytheimage MotorizedstagefromRenishawforchemicalmapping Thisisadrugtablet Theyellowcorrespondstotheactiveingredient Particlesareinthe10 sof mrange ChemicalImaging Nowdefocusthelaser notasmallspotbutrather baths thesampleinlaserradiation Passtheemittedradiationthroughanarrowbandpassfilter adjustedtoaparticularwavelength chosentobeacertainRamanband FocusthislightontheCCDcamera BrightregionscorrespondtolocationsofsubstancegivingrisetoRamansignal Mixtureofcocaineandsugar Brightspotsarecocaine Applications ArtRestoration This12centuryfrescoonachurchwallinItalyneededtoberestored Whatpaintstouse Ramananalysisclearlyidentifiedthepaintsandpigmentsthatwereoriginallypresent permittingacorrectchoiceofcleaningmaterialsandsubsequentrepaintingtorestoreitsoriginalcondition Applications PaintChips Forensicanalysisofpaintchipsinvehicleaccidents Oftenmultiplelayers CananalyzewithIRbystrippingsuccessivelayers ImageedgewithmicroRaman Layers1and3turnedouttoberutilephaseTiO2 awhitepaint Layer2wasaGoethite aredpigmentandcorrosioninhibitor Layer4wasmolybdateorange acommonredpaintinthe70 sinNorthAmericaandstillusedintheU K today Layer5wasasilicatebasedpaint DataarisingfromacaseinvestigatedbyLAPD Applications GemForgery In1999anewprocesswasdeveloped calledGEPOL wherebybrowntypeIIadiamondscouldbetreatedtobecomeindistinguishablefromnaturallycleardiamonds Ramanpresentedwaytodistinguishthem Applications BulletProofGlass Identifypoly carbonate frompoly methylmethacrylate Bothusedforshatter proofglass Applications SunscreenFormulations Herearethespectraof5commonsunscreeningredients 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 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(qiáng)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 傅立葉變換 拉曼光譜儀 FT Ramanspectroscopy光源 Nd YAG釔鋁石榴石激光器 1 064 m 檢測器 高靈敏度的銦鎵砷探頭 特點(diǎn) 1 避免了熒光干擾 2 精度高 3 消除了瑞利譜線 4 測量速度快 Sources Sources 1 ExperimentusedtorequireconsiderableexcitationpowerIonlasers 40WcwHe Ne 10WcwYAG 1J 10nspulse 100MWaveragepulse Butdetectorshaveimprovedsomuch thesourcepowerrequirementshavebeendecreased Diodelaser 25mWotherlaserscanbemadecorrespondinglysmaller Detectors Scatteredlightislowintensity sohighgainPMT shavebeenusedinthepast ThiswasusedforscannedandFT Ramaninstrumentationformanyyears NowcooledCCDarraysareused experimentisnowmultichannel CooledNIRdetector 1024x256pixelarray 26 msquarepixels FromJobinYvon