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1、UV-Vis(Absorption)Spectrometry(Chapters13,14)Beer'sLaw:II0A=ebc=-logT=-log=logI0IAbsorbanceisadditiveAtotal=A1+A2...=e1bc1+e2bc2...ina2componentmixtureAl1=e1,l1×b×c1+e2,l1×b×c2Al2=e1,l2×b×c1+e2,l2×b×c2LimitationsofBeer'sLaw(pp303-311):(1)Chemicaleffects-analyteassociates,dissociat
2、esorreactstogivemoleculewithdifferenteFig13-3CEM333page4.1(2)Physicaleffects-straylight,polychromaticradiationornoiseAl=-logTl=elbc111æI0ö=logç÷èIøl1-el1bcI=I10l10l1-ebcl2Il2=I0l210æI+IöA=ç0l10l2÷lçI+I÷èl1l2øæöI+Iç0l10l2÷=ççI10-el1bc+I10-el2bc÷÷è0l10l2ø-el1bc-el2bcAl=log(I0l1+I0l2
3、)-log(I0l110+I0l210)CEM333page4.2®non-linearcalibrationcurve(Fig13-4,13-5)CEM333page4.3TypicalUV-VisSpectrophotometers:(Fig13-12)includeslselection(a)singlebeam(SB)(b)double-beam(DB)-in-space(c)double-beam-in-timeCEM333page4.4MultichannelSpectrophotometerNomonochromator,butdispers
4、estransmittedlightandmeasures"allwavelengthsatonce"(Fig13-13)Noscanning-simpleandfastMoreexpensiveLimitedresolutionCEM333page4.5ApplicationsofUV-VisSpectrometry:excitation*relaxationM+hu¾¾¾¾¾®M¾¾¾¾¾®M+hu/heatHowprobable?eranges0to~100,000L/molácm"forbidden""allowed"electronictrans
5、itionWhichelectronsgetexcited?InUV-Vis,photonprovidesenoughenergytomoveoutervalence(bonding)electronsOrganicmoleculesys=ys+ysBondingsmolecularorbitalAB*y*=ys-ysAntibondingsmolecularorbitalsAByp=yp+ypBondingpmolecularorbitalAB*y*=yp-ypAntibondingpmolecularorbitalpABFig14-1CEM333pag
6、e4.6s,p(bonding)andn(non-bonding)electronsFig14-2Arrangeintermsofenergy:Fig14-3s®s*DElarge(l<150nm)e=10-10,000L/molácmn®s*(halogens,N,O,S)DEsmaller(l=150-250nm)e=200-2000L/molácmp®p*n®p*DEsmall(l=200-700nm)e=10-10,000L/molácmIdealforUV-VisspectrometryoforganicchromophoreCEM333page
7、4.7¥RedshiftoflmaxwithincreasingconjugationCH2=CHCH2CH2CH=CH2lmax=185nmCH2=CHCH=CH2lmax=217nm¥Redshiftoflmaxwith#ofringsBenzenelmax=204nmNaphthalenelmax=286nm¥BlurredwithsolventFig14-5CEM333page4.8InorganicIonsMosttransitionmetalionsarecolored(absorbinUV-vis)duetod®delectronictran
8、sitions(Fig14-7)Remember:¥Solutio
