电子顺磁共振Electron Paramagnetic Resonance本课程内容电子顺磁共振研究对象二. 电子顺磁共振基本原理三. 电子顺磁共振波谱电子顺磁共振的应用电子顺磁共振研究对象固体碱金属碱金属的核外价电子：nS】自由基(radical)含有一个未成对电子的化合物。如：CH3, SP3杂化;二苯基苦基月井基(DPPH) Diphenyl Picryl HydrazylPh、PhDPPH的ESR谱线:其它相关的自由基化学:Free radicals in food*.BSR signals from potato chips, produced ty 8 difYercni company.Sample volume; 2.00 rng.Oil degradationESR spectra obtained in UV-irradiating to salad-oil. at -120cC (a) in the air, (b) under vacuum.Coffee BeanESR SignalPBN Spin AdductsLag PhasLag Time*酒类：啤酒主要性能指标之一，lagtimeBeer flavor stability Judged with the amount of OH produced as the indexOxidative Forcing Test at 60*C (min)Beer-Flavor Stability活性氧:Activated OxygenGeneration of Active Oxygen1. Reduction of O2 by enzymesXanthine oxidase - O2*2. Auto-Oxidation of chemical substancesEpinephrine Paraquat o2-, OH t H2O23. Radiation or (JV irradiationRadiation to H2O - 02, OH , H2O2UV excitation of coloring matter- O 八 OH4. Oxidation of unsaturated fatty acid-L, LO, LOONAOPHNADP1OxygenPeroxideMetalUVRadiationStressShockIschemiaJlqohO3 a三7厂酉I ProtectionV.CV.ESOD Catalase Glutathione(LQ- ( 2)Brain DamageHeart DiseaseLung DiseaseGastral DiseaseSkin DisorderAgingCancerInflammationActive OxygenA/Aaz(e) 250nM SOD亠-VParamagnetic substancesholding more than one unpaired electronH C H三重态分子其分子轨道上有两个未偶电子，但其与双基不同，这两 个电子彼此相距很近，有很强的相互作用。1、激发三重态；如：蔡激发三重态;2、基态就是三重态分子如：氧分子。|0.0FFfiURE 62 lie Mate energies of adf tuo凸thbixing an exdi&ngeuiiersctKMk few J| 0. When /0 Z posiiive. the:mjgl识 saw Its low-ex in 口uagy过渡金属和稀土元素The electronic state forthe ground state of the 3d series free metal ion.SpeciesTi(ni) V(III) Cr(Ul)Crdl) pjiijFedl) Co(ll) Ni(II) Cu(ll) Cud)n : dn12345678910Mz210-1-2-4TT卄卄卄卄卄 + + +亠卄卄卄卄 -4THr 卄卄 H-H- -44Hrs% 1 % 2 % 2 % 1 % 0过渡金属、稀土元素具有未充满的3cl, 4d, 51及4f壳层, 核外有一个或一个以上的未成对电子。V23(4S23d3)V5+（3d）无EPR信号V4+（3d1）有EPR信号Mn25 (4S23d5)Mn5+ (3d)无EPR信号Mn2+(3d 5)有EPR信号过渡金属和稀土元素的EPR谱线特点:谱线复杂且谱线大多很宽，理论处理也较困难。原因：1、电子处在离子的1壳层中，它们的自旋运动和轨运动间有 很强的自旋一轨道偶合作用；2、离子并非以自由形式存在，处在由配位体组成的晶场中。半导体中的空穴或电子可用EPR来作定量研究。晶格缺陷如：V心：The positive-ion vacancy (V center)V - center (earlier called VI) (tetiagonal symmetiy )F心：an election in a negative-ion vacancy (F center) hi an alkali halide (Cubic symmetiy )325330335340345350Magnetic Field / mTMagnetic Field/mTEPR的优点与缺点:优点:1、EPR是观察自由基等顺礒性物质的一种最直接、高灵敏的方法（与NMR比）;不需对样品进行复杂的处理，直接检测而不破坏样品。缺点：1、局限性大。只能检测顺磁性物质;2、对含有顺磁性离子或原子的化合物,EPR般只能给出较少的局部结构信息，或得 到结构方面的信息复杂，难以作出准确的判定。电子顺磁共振(Electron Paramagnetic Resonance 简称EPR)或称电子自旋共振(Electron Spin Resonance 简称ESR)直接检测和研究含有未成对电子的顺磁性物质电子的磁共振电子自旋磁矩的磁共振包子轨道磁矩的磁共振二.电子顺磁共振基本原理! 物质的顺磁性是由分子的永久磁矩引起的保里原理：每个分子轨道上不能存在两个自旋态相同的电子， 因而各个轨道上已成对的电子自旋运动产生的磁矩 是相互抵消的，只有存在未成对电子的物质才具有 永久磁矩，它在外磁场中呈现顺磁性。电子自旋产生自旋磁矩s=gePP：玻尔磁子霞：无量纲因子，称为g因子由电子的g因子为g=2.0023单个电子磁矩在磁场方向分量g=l/2gep 外磁场H的作用下，只能有两个可能的能量状态:即 E= l/2gPH磁矩M与外磁场H的相互作用Ea=l/2gPHEp=-l/2gPH电子自旋能级与磁场强度的函数关系 Ho为共振时的外磁场能量差 E = gpH这种现象称为塞曼分裂(Zeeman splitting)如果在垂直于H的方向上施加频率为hi)的电磁波,当满足下面条件hv = gPH处于两能级间的电子发生受激跃迁，导致部分处于低能级中的电子吸收电磁波的能量跃迁到高能级中顺磁共振现象受激跃迁产生的吸收信号经电子学系统处理可得到EPR吸收 谱线，EPR波谱仪记录的吸收信号一般是一次微分线型，或 称：一次微分谱线ESR and NMR are very different methods!electronprotonratioRest massme =9.1094*1028gmp=1.6726*1 (T24g5.446*10-4Chargee=-4.80286*10wESUe=4.8O286*1(T1oESU-1Angular momentumh/4兀h/47v1Magnetic dipole mome ntMs=-9eeS g = 2.002322 me=eh/4nmec = 9.274*10-21 erg/G5.58565.0504*10-24 erg/G1836.12Frequency: Factor 1000 larger in EPR ! (GHz instead of MHz)Coupling strength: Factor 1 000 000 larger in EPR ! (MHz instead of Hz) Relaxation Times: Factor 1000 000 smaller in EPR ! (ns instead of ms) =much higher techniqual requirements】 but unique sensitivity to molecular motionSensitivity: Factor 1 000 000 better than in NMR ! (1nM instead of 1mM) An ideal case, though三.电子顺磁共振波谱g 因子AE = hu = g/3HThe field at each spin in flue need by local magn etic fields, no t just the exter nal field :Heft = H + Hlocal SO Heff = (1-s)H = (g/ge)H-This field is induced by H, and so depends on the external field H-g is an effective Zeeman factor, shifted from the electron