拉曼光谱ppt2

SomeRamanAdvantagesHerearesomereasonswhysomeonewouldprefertouseRamanSpectroscopy.•Non-destructivetosamples(minimalsampleprep)•Highertemperaturestudiespossible(don’tcareaboutIRradiation)•Easilyexaminelowwavenumberregion:100cm-1readilyachieved.•Bettermicroscopy;usingvisiblelightsocanfocusmoretightly.•Easysampleprep:waterisanexcellentsolventforRaman.Canprobesamplethroughtransparentcontainers(glassorplasticbag).WatchforFluorescenceSpectrumofanthracene.A:usingAr+laserat514.5nm.B:usingNd:YAGlaserat1064nm.Wanttouseshortwavelengthbecausescatteringdependson4thpoweroffrequency.…BUT…Wanttouselongwavelengthtominimizechanceofinducingfluorescence.SelectionRuleforRamanScatteringMustbechangeinpolarizabilityNon-PolargroupssuchasC-S,S-S,C=C,CC(triplebond),N=Nandheavyatoms(I,Br,Hg)strongscatterersSymmetricstretchingvibrationsaremuchstrongerscatterersthanasymmetricstretchingvibrations对称中心分子CO2，CS2等，选律不相容。无对称中心分子（例如SO2等），三种振动既是红外活性振动，又是拉曼活性振动。选律SCSSCSSCS1234拉曼活性红外活性红外活性振动自由度：3N-4=4拉曼光谱—源于极化率变化红外光谱—源于偶极矩变化PolarizationEffectsPolarizationofCCl4PolarizationofCHCl3Raman位移对不同物质：不同；对同一物质：与入射光频率无关；表征分子振-转能级的特征物理量；定性与结构分析的依据；Raman散射的产生：光电场E中，分子产生诱导偶极距=E分子极化率；由拉曼光谱可以获得有机化合物的各种结构信息：2）红外光谱中，由CN，C=S，S-H伸缩振动产生的谱带一般较弱或强度可变，而在拉曼光谱中则是强谱带。3）环状化合物的对称呼吸振动常常是最强的拉曼谱带。1）同种分子的非极性键S-S，C=C，N=N，CC产生强拉曼谱带，随单键双键三键谱带强度增加。拉曼光谱与有机结构4）在拉曼光谱中，X=Y=Z，C=N=C，O=C=O-这类键的对称伸缩振动是强谱带，反这类键的对称伸缩振动是弱谱带。红外光谱与此相反。5）C-C伸缩振动在拉曼光谱中是强谱带。6）醇和烷烃的拉曼光谱是相似的：I.C-O键与C-C键的力常数或键的强度没有很大差别。II.羟基和甲基的质量仅相差2单位。III.与C-H和N-H谱带比较，O-H拉曼谱带较弱。Vibrationalmodesofmethane(CCl4)Infraredinactive,RamanactivevibrationsInfraredactive,Ramaninactivevibrations314cm-1776cm-1463cm-1219cm-1InfraredandRamanSpectrumofCCl4776cm-1314cm-1463cm-1219cm-1InfraredspectrumRamanspectrum2941，2927cm-1ASCH22854cm-1SCH21029cm-1（C-C）803cm-1环呼吸1444，1267cm-1CH23060cm-1r-H)1600,1587cm-1c=c)苯环1000cm-1环呼吸787cm-1环变形1039,1022cm-1单取代RamanSpectroscopy•Relativelysimpleandnon-destructivestructureanalysistechniqueofcarbonmaterials•Powerfultoolforthestructuralcharacterizationofdiamondoramorphouscarbonmaterials.5001000150020002500Intensity(a.u.)RamanShift(cm-1)5001000150020002500G-modeDiamond:1335.5cm-1Intensity(a.u)RamanShift(cm-1)DLCDiamondNSOMRamanImagingSpectrumofpotassiumtitanylphosphate.FromHansHallenatNCSU.Squaresare5x5µmsquareofthismaterialdopedwithRb.Anear-fieldscanningmicroscopewasusedandtheRamansignalwasusedtokeythesubstrateresponse.ChemicalMappingFocuslasertosmallspot.TunespectrometertoparticularRamantransitionpeak.Rasterscanthesampleunderthelaserbeam,recordintensitychanges.Resultantmapcorrelateswithsubstance.Acquireanentirespectrumateverypoint,thenchoosethefeaturewithwhichtokeytheimage.MotorizedstagefromRenishawforchemicalmapping.Thisisadrugtablet.Theyellowcorrespondstotheactiveingredient.Particlesareinthe10’sofµmrange.ChemicalImagingNowdefocusthelaser(notasmallspotbutrather“baths”thesampleinlaserradiation).Passtheemittedradiationthroughanarrowbandpassfilter,adjustedtoaparticularwavelength,chosentobeacertainRamanband.FocusthislightontheCCDcamera.BrightregionscorrespondtolocationsofsubstancegivingrisetoRamansignal.Mixtureofcocaineandsugar.Brightspotsarecocaine.