自旋动力学-第三章课件

NMR谱特征：位置，形状，宽窄影响因素

提供分子结构、运动信息NMR谱（频域）：I()第三章：核磁共振谱Chapter3NMRSpectroscopyI强度随频率分布3.1简单脉冲序列

（SimplePulseSequence）sfid(t)=

Meqexp(iω0t)exp{−t/T2}fouriertransformationt

T2,1/T2:transverserelaxationtime,rateExperimentalT2:Fidorlinewidth

FID(时域）NMR谱(频域）匀场？frequency,11/2Fullwidthathalf-height.absorptionLorentzianangularfrequency,Fullwidthathalf-height=1/(T2)~1/T2relaxation

rate

3.2SimplespectrumFIDDecay:指数衰减：xp{−t/T2}

Lorentzian吸收线型线宽3.3SpectralFrequencies3.3谱频率(labframe静止):ref00Cos(reft)RelativeSpectralFrequencies:0=ω0−ωref

=ω−ωreftheresonanceoffsetortheLarmorfrequencyintherotatingframeRelativeSpectralFrequencies:CaseofPositiveGyromagneticRatio3.4相对谱频率(rotatingframe旋转):3.5InhomogeneousBroadeningDifficult:aperfectlyhomogeneousmagneticfieldThesampleitselftendstodistorttheappliedmagneticfield,becauseofitsmagneticsusceptibility.

*InsomeNMRexperiments,spatiallydependentmagneticfieldsaredeliberatelyapplied,usingspeciallydesignedadditionalfieldcoils.Thisisthecasein,forexample,NMRimagingexperiments.非均匀宽化500*106Hz/11.7T=4274Hz/G=0.4Hz/0.0001G500MHz(11.7T)谱仪0.4HzB~0.0001G磁场均匀度例1：不均匀磁场（外磁场，样品（外部形状，内部空洞等））purewaterχ=−9.05×10−6.Binduced=-0M=-B0~1G形状各向异性因子=4,4/3,….0Binduced=-0MM非均匀退磁场BinducedB0InhomogeneousBroadening样品不同位置，取向，化学环境等rf照射Burningahole烧个洞

非均匀宽化化学位移各向异性Thechemicalshiftδscalealwaysincreasesfromrighttoleftinplottedspectra.106（ppm)40ppm40X100(Hz)400MHz谱仪DefinitionReference1H与磁场无关Couplewithnequivalentnuclei:1H:2nI+1=(n+1)splittingr=0,1,…n与N个等价核（l=1/2)偶合:2Nl+1

peaks(2nI+1)分裂0,J(Hz)JItotal=1，0Itotal=I1+I2….Abs(I1-I2)两个角动量组合：2D:自旋I=11storderapproximationi.CouplewithN-nonequivalentnuclei:(I=1/2)splitto2Nii.Couplewithnequivalentnuclei:(n+1)(2nI+1)Coefficientsofbinominalexpansion(relativeintensity)iii.CenterνiSplitingJiv.noJsplittinginspectrabetweenequivalentnuclei3.9HeteronuclearDecoupling13CspectrumoftheCH2regioninethanol.HCH3CH2exchange-decoupling异核去偶rfHCH2射频异核去偶“Improved”Stern-GerlachExperimentSpin½particle(e.g.silveratoms)Wha