红外与拉曼光谱入门.pdf

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1、第第二二章章分子振动光谱分子振动光谱------红外红外光谱光谱与拉曼与拉曼光谱光谱------IRandRamanIRandRamanWilliamHerschelAround1800,Herschelstudiedthespectrumofsunlightusingaprism.Hemeasuredthetemperatureofeachcolor,andfoundthehighesttemperaturewasjustbeyondthered,whatwenowcallthe'infrared'.TheScienceMuseum,UKTheInfraredPart

2、oftheEMSpectrumSoccerFieldHouseBacteriaVirusProteinBaseballCellWAVELENGTHThisPeriodWaterMoleculeSIZEWAVELENGTH(inmeters)103102101110-110-210-310-410-510-610-710-810-910-1010-1110-12COMMONNAMERADIOWAVESINFRAREDULTRAVIOLET“HARD”XRAYSMICROWAVES“SOFT”XRAYSGAMMARAYSFREQUENCY(wavespersecond)67

3、891011121314151617181019201010101010101010101010101010ENERGYOFONEPHOTON(electronvolts)-9-8-7-6-5-4-3-2-11234561010101010101010101101010101010IRunits:wavenumbers(cm-1),Near-IR:4000–14000cm-1-1Mid-IR:500–4000cm-110micronwavelength=1000cm-1Far-IR:5–500cm-11eV≈8100cm1THz≈33cm-1IRcovers~1meVt

4、o1eV300Kelvin≈210cm-1红外摄影§§1.1.基本原理基本原理1.1.红外吸收与分子的简谐振动(normalvibration)Energy--structurerelationship简谐振动:AB1ν=kv2πµµ−1=Μ-1+M-1AB振动频率ν与折合质量µ与化学键的键力常数k有关v即与化合物组成和结构有关WhatcanwelearnfromIR？•AtomsvibratewithfrequenciesintheIRrange•化学分析:•Matchspectratoknowndatabases–Identifyinganunknowncompou

5、nd,Forensics,etc.•Monitorchemicalreactionsin-situ•结构分析:•Candeterminewhatchemicalgroupsareinaspecificcompound•ElectronicInformation:•Measureopticalconductivity–DetermineifMetal,Insulator,Superconductor,Semiconductor–BandGaps,Drudemodel区别于紫外－可见光谱AB引起振动能级的跃迁hν电磁波导致分子振动，偶极距发生变化，偶极子转动发射电磁波激发态

6、分子振动形式电子Stretching&Bending能级Scissoringrocking基态waggingIRtwistingEg.CH2stretchingstretchingscissoringwaggingtwistingrockingAnExample:CO2OCOIRAbsorbenceSymmetricStretch(Dipolemoment=0sonotIRactive)AsymmetricStretch(HasdipolemomentsoIRactive)BendingMode(HasdipolemomentsoIRactive)Wavenumber(

7、cm-1)ADipoleMoment=chargeimbalanceinthemolecule描述一个分子所需要的自由度（三维空间内）y一个点:3自由度N个点:3N自由度分子在空间的运动包括：3Nfreedom整个分子重心的平动(3freedom)整个分子绕其重心的转动(3freedom)zx每个原子相对于其它原子的运动（振动）OHOH3N-63N-5HO(linearmolecule)HHHHOHOHOH1.2.1.2.拉曼拉曼光谱原理光谱原理当光照射到物质上时会发生非弹性散射，散射光中除有与激发光波长相同的弹性成分（瑞利散射）外，还有