拉曼光譜分析法

1、拉曼光譜分析法拉曼光譜分析法劉和文Remote Raman Analysis on Planetary MissionslTo allow Raman spectroscopy at range of 10s of meters.lThis NASA-funded project is aimed at Mars landers or landers on other planets, but also has terrestrial uses. 激光拉曼光譜基本原理激光拉曼光譜基本原理Rayleigh散射：散射： 彈性碰撞；無(wú)能量交換，僅改變方向；Raman散射：散射： 非彈性碰撞；方向改變

2、且有能量交換；Rayleigh散射散射Raman散射散射E0基態(tài)， E1振動(dòng)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Raman C V 發(fā)現(xiàn)；1960年快速發(fā)展） h E0E1V=1V=0h 0h 0h 0h 0 + E1 + h 0E0 + h 0h( 0 - )激發(fā)虛態(tài)基本原理基本原理1 1. Raman. Raman散射散射Raman散射的兩種躍遷能量差： E=h( 0 - )產(chǎn)生產(chǎn)生stokes線；強(qiáng)線；強(qiáng)；基態(tài)分子多；基態(tài)分子多； E=h( 0 + )產(chǎn)生反產(chǎn)生反stokes線；線；弱；弱；Raman位移：位移：

3、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 - )Rayleigh / Raman TransitionsIR AbsorptionsRayleigh / Raman Transitions and SpectraRayleigh / Raman Transitions and SpectraThe SpectrumA complete Raman spectrum consists of: a Rayleigh scattered peak (

4、high intensity, same wavelength as excitation) a series of Stokes-shifted peaks (low intensity, longer wavelength) a series of anti-Stokes shifted peaks (still lower intensity, shorter wavelength) spectrum independent of excitation wavelength (488, 632.8, or 1064 nm)Spectrum of CCl4, using an Ar+ la

5、ser at 488 nm.Raman SpectroscopyAnother spectroscopic technique which probes the rovibrational structure of molecules.C.V. Raman discovered in 1928; received Nobel Prize in 1931.Can probe gases, liquids, and solids.Must use a laser source for excitation.Resurgence in recent years due to the developm

6、ent of new detectors with improved sensitivity.Shift back away from FT-Raman to dispersive Raman with multichannel detector systems.Infrared and Raman Spectra of BenzeneIRRaman拉曼光譜與紅外光譜分析方法比較拉曼光譜與紅外光譜分析方法比較拉曼光譜拉曼光譜紅外光譜紅外光譜光譜范圍光譜范圍40-4000Cm-1光譜范圍光譜范圍400-4000Cm-1水可作為溶劑水可作為溶劑水不能作為溶劑水不能作為溶劑樣品可盛于玻璃瓶，毛細(xì)管等

7、容器樣品可盛于玻璃瓶，毛細(xì)管等容器中直接測(cè)定中直接測(cè)定不能用玻璃容器測(cè)定不能用玻璃容器測(cè)定固體樣品可直接測(cè)定固體樣品可直接測(cè)定需要研磨制成需要研磨制成 KBR 壓片壓片Some Raman AdvantagesHere are some reasons why someone would prefer to use Raman Spectroscopy. Non-destructive to samples (minimal sample prep) Higher temperature studies possible (dont care about IR radiation) Easil

8、y examine low wavenumber region: 100 cm-1 readily achieved. Better microscopy; using visible light so can focus more tightly. Easy sample prep: water is an excellent solvent for Raman. Can probe sample through transparent containers (glass or plastic bag).Watch for FluorescenceSpectrum of anthracene

9、. A: using Ar+ laser at 514.5 nm. B: using Nd:YAG laser at 1064 nm.Want to use short wavelength because scattering depends on 4th power of frequency.BUTWant to use long wavelength to minimize chance of inducing fluorescence.紅外活性和拉曼活性振動(dòng)紅外活性和拉曼活性振動(dòng)紅外活性振動(dòng)紅外活性振動(dòng) 永久永久偶極矩；極性基團(tuán)；偶極矩；極性基團(tuán)； 瞬間偶極矩；非對(duì)稱(chēng)分子；瞬間偶極矩；

10、非對(duì)稱(chēng)分子；紅外活性振動(dòng)紅外活性振動(dòng)伴有伴有偶極矩變化的振動(dòng)可以偶極矩變化的振動(dòng)可以產(chǎn)生紅外吸收譜帶產(chǎn)生紅外吸收譜帶. .拉曼活性振動(dòng)拉曼活性振動(dòng) 誘導(dǎo)誘導(dǎo)偶極矩偶極矩 = E 非極性基團(tuán)，對(duì)稱(chēng)分子；非極性基團(tuán)，對(duì)稱(chēng)分子；拉曼活性振動(dòng)拉曼活性振動(dòng)伴隨有極化率變化的振動(dòng)。伴隨有極化率變化的振動(dòng)。 對(duì)稱(chēng)分子對(duì)稱(chēng)分子： 對(duì)稱(chēng)振動(dòng)對(duì)稱(chēng)振動(dòng)拉曼活性。拉曼活性。 不對(duì)稱(chēng)振動(dòng)不對(duì)稱(chēng)振動(dòng)紅外活性紅外活性 EeerSelection Rule for Raman ScatteringvMust be change in polarizabilityNon-Polar groups such as C-S, S-

11、S, C=C, CC (triple bond), N=N and heavy atoms (I, Br, Hg) strong scatterersSymmetric stretching vibrations are much stronger scatterers than asymmetric stretching vibrationsPolarization Effects 對(duì)稱(chēng)中心分子對(duì)稱(chēng)中心分子CO2，CS2等，選律不相容。等，選律不相容。 無(wú)對(duì)稱(chēng)中心分子（例如無(wú)對(duì)稱(chēng)中心分子（例如SO2等），三種振動(dòng)既是紅外活等），三種振動(dòng)既是紅外活性振動(dòng)，又是拉曼活性振動(dòng)。性振動(dòng)，又是拉曼活性

12、振動(dòng)。選律選律SCSSCSSCS 1 2 3 4拉曼活性拉曼活性紅外活性紅外活性紅外活性紅外活性振動(dòng)自由度：振動(dòng)自由度：3N- 4 = 4拉曼光譜拉曼光譜源于極化率變化源于極化率變化紅外光譜紅外光譜源于偶極矩變化源于偶極矩變化Polarization of CCl4 Polarization of CHCl3 Raman位移位移 對(duì)不同物質(zhì)： 不同； 對(duì)同一物質(zhì)： 與入射光頻率無(wú)關(guān)；表征分子振-轉(zhuǎn)能級(jí)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(chǎng)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：由拉曼光譜可以獲得有機(jī)化合物的各種結(jié)構(gòu)信

13、息：2）紅外光譜中，由C N，C=S，S-H伸縮振動(dòng)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(duì)稱(chēng)呼吸振動(dòng)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，CC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)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(lèi)鍵的對(duì)稱(chēng)伸縮振動(dòng)是強(qiáng)譜帶，反這類(lèi)鍵的對(duì)稱(chēng)伸縮振動(dòng)是弱譜帶。紅外光譜與此相反。5）C-C伸縮振動(dòng)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(méi)有很大差別。II. 羥基和甲基的質(zhì)量?jī)H相差2單位。 III.

14、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(duì)比紅外與拉曼譜圖對(duì)比紅外光譜：基團(tuán)；紅外光譜：基團(tuán)；拉曼光譜：分子骨架測(cè)定；拉曼光譜：分子骨架測(cè)定；紅外與拉曼譜圖對(duì)比紅外與拉曼譜圖對(duì)比Raman and Infrared Spectra of H-CC-HAsymmetric C-H StretchSymmetric C-H StretchCC StretchVibrational modes of methane (CCl4)Infrared inactive, Raman active vibrationsInfrared active, Raman inactive vib

15、rations314 cm-1776 cm-1463 cm-1219 cm-1Infrared and Raman Spectrum of CCl4776 cm-1314 cm-1463 cm-1219 cm-1Infrared spectrumRaman spectrum2941，2927cm-1 ASCH22854cm-1 SCH21029cm-1 （C-C）803 cm-1環(huán)呼吸環(huán)呼吸 1444，1267 cm-1 CH23060cm-1 r-H)1600,1587cm-1 c=c)苯環(huán)苯環(huán)1000 cm-1環(huán)呼吸環(huán)呼吸787 cm-1環(huán)變形環(huán)變形1039, 1022cm-1單取代單取代

16、Raman SpectroscopylRelatively simple and non-destructive structure analysis technique of carbon materialslPowerful tool for the structural characterization of diamond or amorphous carbon materials.5001000150020002500 Intensity (a.u.)Raman Shift (cm-1)5001000150020002500G-modeDiamond: 1335.5cm-1 Inte

17、nsity(a.u)Raman Shift (cm-1)DLCDiamondRemote Raman Analysis on Planetary MissionslTo allow Raman spectroscopy at range of 10s of meters.lThis NASA-funded project is aimed at Mars landers or landers on other planets, but also has terrestrial uses. NSOM Raman ImagingSpectrum of potassium titanyl phosp

18、hate. From Hans Hallen at NCSU. Squares are 5 x 5 m square of this material doped with Rb. A near-field scanning microscope was used and the Raman signal was used to key the substrate response.Chemical MappingFocus laser to small spot. Tune spectrometer to particular Raman transition peak. Raster sc

19、an the sample under the laser beam, record intensity changes. Resultant map correlates with substance. Acquire an entire spectrum at every point, then choose the feature with which to key the image.Motorized stage from Renishaw for chemical mapping.This is a drug tablet. The yellow corresponds to th

20、e active ingredient. Particles are in the 10s of m range.Chemical ImagingNow defocus the laser (not a small spot but rather “baths” the sample in laser radiation).Pass the emitted radiation through a narrow bandpass filter, adjusted to a particular wavelength, chosen to be a certain Raman band.Focus

21、 this light on the CCD camera. Bright regions correspond to locations of substance giving rise to Raman signal.Mixture of cocaine and sugar. Bright spots are cocaine.Applications - Art RestorationThis12 century fresco on a church wall in Italy needed to be restored. What paints to use?Raman analysis

22、 clearly identified the paints and pigments that were originally present, permitting a correct choice of cleaning materials and subsequent repainting to restore its original condition.Applications - Paint ChipsForensic analysis of paint chips in vehicle accidents. Often multiple layers. Can analyze

23、with IR by stripping successive layers. Image edge with microRaman.Layers 1 and 3 turned out to be rutile phase TiO2 - a white paint. Layer 2 was a Goethite, a red pigment and corrosion inhibitor. Layer 4 was molybdate orange, a common red paint in the 70s in North America and still used in the U.K.

24、 today. Layer 5 was a silicate based paint. Data arising from a case investigated by LAPD.Applications - Gem ForgeryIn 1999 a new process was developed called GE POL whereby brown type IIa diamonds could be treated to become indistinguishable from naturally clear diamonds. Raman presented way to dis

25、tinguish them.Naturally clear diamondOriginally brown diamondApplications - Bullet Proof GlassIdentify poly(carbonate) from poly(methylmethacrylate).Both used for shatter-proof glassApplications - Sunscreen FormulationsHere are the spectra of 5 common sunscreen ingredients. Raman is able to determin

26、e from a spectrum on the arm the nature of the sunscreen being used.A: ODPABA (octyl N,N-dimethyl-p-aminobenzoic acid)B: OMC (octyl p-methoxycinnamate)C: BZ3 (oxybenzone)D: OCS (octyl salicylate)E: DBM (dibenzoylmethane)G.R. Luppnow et al., J. Raman. Spec. 34, 743 (2003).激光激光Raman光譜儀光譜儀 laser Raman

27、spectroscopy激光光源激光光源：He-Ne激光器，波長(zhǎng)632.8nm； Ar激光器， 波長(zhǎng)514.5nm， 488.0nm； 散射強(qiáng)度1/4 單色器單色器： 光柵，多單色器； 檢測(cè)器檢測(cè)器： 光電倍增管， 光子計(jì)數(shù)器；傅立葉變換-拉曼光譜儀FT-Raman spectroscopy光源：光源：Nd-YAG釔鋁石榴石激光器（1.064m）；檢測(cè)器：檢測(cè)器：高靈敏度的銦鎵砷探頭；特點(diǎn)：特點(diǎn)：（1）避免了熒光干擾；）避免了熒光干擾；（2）精度高；）精度高；（3）消除了瑞利譜線；）消除了瑞利譜線；（4）測(cè)量速度快。）測(cè)量速度快。SourcesRaman intensity is weak and the excitation source must be strong to generate sufficient signal.Source must be monochromatic so that spectrum is sufficiently uncomplicated.Intense lamps can work, but when monochromatized, have very little power.Scattering efficiency increases as 4: the bluer the light, th