《材料测试技术及方法》课程教学资源（讲稿）1-材料现代分析方法_1-上课课件_11-2 电磁辐射与材料的相互作用-分子光谱

第五章紫外可见吸收光谱分析12、电子辐射与材料相互作用（1）分子的散射p25(2）紫外、可见（吸收）光谱p29p30~31（3）分子荧光、磷光光谱3、紫外可见吸收光谱法之基本原理p204209

1 第五章 紫外可见吸收光谱分析 l 2、电子辐射与材料相互作用 （1）分子的散射p25 （2）紫外、可见（吸收）光谱p29 （3）分子荧光、磷光光谱 p30~31 l 3、紫外可见吸收光谱法 之 基本原理p204~209

2、电子辐射与材料相互作用辐射的散射指电磁辐射(与物质发生相互作用)部分偏离原入射方向而分散传播的现象物质中与入射的辐射即入射线相互作用而致其散射的基本单元可称散射基元「散射基元是实物粒子，可能是分子、原子中的电子等，取决于物质结构及入射线波长大小等因素

2 2、电子辐射与材料相互作用 l 辐射的散射指电磁辐射(与物质发生相互作用) 部分偏离原入射方向而分散传播的现象。 l 物质中与入射的辐射即入射线相互作用而致其 散射的基本单元可称散射基元。 l 散射基元是实物粒子，可能是分子、原子中的 电子等，取决于物质结构及入射线波长大小等 因素

(1)分子散射瑞利散射弹性散射2=>0分子散射拉曼散射非弹性散射 2>+入0反斯托克斯线 入<>拉曼散射谱斯托克斯线 >>入0拉曼散射产生的实质-入射光子与分子作用时分子的振动能级或转动能级跃迁3

3 (1) 分子散射 瑞利散射￾￾￾￾弹性散射 λ=λ0 分子散射 ￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾￾拉曼散射￾￾￾非弹性散射 λ≠λ0 反斯托克斯线 λλ0 拉曼散射产生的实质-入射光子与分子作用时分 子的振动能级或转动能级跃迁

Anti-Stocks线Stocks线32咔动能子基级0Raman散射Rayleigh散射

4 0 1 2 3 e 电 子 基 态 振 动 能 级 e e Rayleigh 散射 e e e Raman 散射 Stocks线 Anti-Stocks线

CC1 4 的拉曼光谱Rayleighscattering-459Stockslinesanti-Stockes-314lines-218218314459-400-2000200400Av/cm-l

5 CCl4的拉曼光谱 Stocks lines anti-Stockes lines Rayleigh scattering Δν/cm-1

Box17-3RayleighandRamanScatteringEmission spectra can exhibit confusing features in addition toThe second strongest peak in this example comes at 800 nm,fluorescence and phosphorescence.The chart shows an emissionwhich is exactly twice the excitation wavelength. It is an artifact ofspectrum ofaqueous dichlorofluorescein(colored line)and,forrefer-the monochromator.Grating monochromators designed topasswavelength入alsopass integerfractions/2,/3,and soon,withence,an emission spectrumofpure water(black line).The excitationwavelength is 400 nm. The only difference between the two traces isdecreasing efficiency.When the emission monochromator in Figurefluorescence from dichlorofluorescein with a peak at 522 nm.17-21 is set to pass 800 nm. it also passes some light at 400 nm.Rayleigh scattering at 400nmpasses through the monochromatorRayleighsetto 800nm.We call this second-orderdiffraction fromthemono-scattering(400 nm)chromator. If we used a filter to block 400-nm light between the2nd ordergrating line.sample cell and the emission monochromator in Figure 17-21, therefrom Rayleighoeewouldbenopeakat800nmintheemissionspectrum.二氯荧光素scatteringA weak, but reproducible,peak is observed in both water and(800 nm)dichlorofluorescein solution at 462 nm. The difference in energyRamanFluorescencefromscatteringdichlorofiuoresceinbetween incident light at 400 nm and the peak at 462 nm correspondsfromH,o(522 nm)toavibrationalenergyof H,O.Thepeak at462nm is calledRaman(462 nm)scattering after the Indian physicist C, V.Raman, who discoveredthis phenomenon in 1928 and was awarded the Nobel Prize in 1930.In this type of scattering,which also occurs in a time frame of-10-15s,a smallfraction ofincidentphotons gives up one quantum600400500700800of molecular vibrational energy to H2O.Scatteredradiation emergesEmission wavelength (nm)with less energy than the excitation energy. Vibrational energy is cus-Uppertrace: Emission spectrum of aqueous dichlorofluorescein.Lowertomarily expressed as thewavenumber (cm)of aphoton with thattroce:Spectrum observed from purewater.[CourtesyKris Varazo, Francisenergy.Liquid H,O has a broad range of vibrational energies cen-Marion UnieeR.J.ClatkandA.Oprysaa,FluorescenceandLightScatteringtered near 3404 cm-.Thewavenumber of the exciting radiation is1.Chem.Ed.2004,87,7051/wavelength =1/400 nm =25 000 cm1.In Raman scattering,anWhat are the other peaks? The strongest peak, which is off-incidentphotonwithenergyof25000cm-givesup3404cmscale, is observed at the excitation wavelength of 400 nm.It isand emerges at (25000-3404)=21596 cm1.The wavelength iscalled Rayleigh scattering after the same Lord Rayleigh (J. W.1/(21596 cm-)463nm.Theobservedpeak is at 462nm.Strutt) who discovered argon (page 76). The oscillating electro-What are the lessons from this example? First, compare themagnetic field of the excitation light source causes electrons inspectrum ofpure solvent to the spectrum of a sampleunder study sowater molecules to oscillate at the same frequency as the incidentthat you can disregard peaks due to solvent,Second, fluorescenceradiation. Oscillating electrons emit this same frequency of radia-comes at a fixed location, such as 522 nm for dichlorofluorescein.tion in all directions. The time required for scattering is essentiallyThe wavelength of scattered radiation varies with incident wave-the period of one oscillation of the incoming electromagneticlength.If weusedan excitation wavelengthof 410nminsteadofwave,which is-10-15sfor400-nmlight.Bycomparison,thetime400,thesecond-ordergratinglinewould beseen at820nm and thefor fluorescenceis-10-to 10-s.Rayleigh scattering is alwayswater Raman line would be at an energy that is3404cmless than6present and is usually filtered out so that it is not displayed in thethe exciting light, or 477 nm. Scattered radiation shifts with theemission spectrum.incident wavelength,butfluorescence andphosphorescence do not

6 二氯荧光素

1852年Stokesshift of quinine(奎宁)in CambridgeSolutionof quinineEmission filterExcitation(yellow-glassofwine)filter400nmTransmits>400nm(blue-glassfromchurch window)G.G.StokesFigure1.6.Experinuentai schematicfordetection oftheStokes'shift

1852年Stokes’ shift of quinine (奎宁) in Cambridge 7

硫酸奎宁荧光素WAVELENGTH(nm)6:00250320350400440450520$103T71.010Cuinine SulfateHOOHin1MH5066C-1o.,5-AbsorptionEmissionEm.NCSEXC.300400500600355003150027500235001950015500WAVENUMBER (cm-1)8

硫酸奎宁 8 荧光素

吸收峰与发射峰之间的能级差：21(me- m)n2-1e-l+ cons tan tnA-nF32n2-hc 2e +1 +1a（折射率)，depends onI n: refractive indexthe motion of electrons within the solventmolecules, essentially instantaneous andcan occur during light absorption(介电常数) ε : dielectricconstantdepends on both electronic and molecularmotions,thelatterbeingsolventreorganization around the excited state

吸收峰与发射峰之间的能级差： l n: refractive index (折射率), depends on the motion of electrons within the solvent molecules, essentially instantaneous and can occur during light absorption l ε: dielectric constant (介 电 常 数 ), depends on both electronic and molecular motions, the latter being solvent reorganization around the excited state. 9

Excitedstatee>gSotvent(V(.)reaxatontueArt(n)Ground stateT(E)Gas phaseInsolutionFieure 6.5.Effects of tie nefractive inmdex (n) and dielectric Constant(e)ontheabsorption and emaission energies.21-m.ne+ cons tantnA-nhc2n?eoru+12e+a10Dipoleinadie

Ground state 10 Excited state