分析化学英文课件CH19 UV-vis.ppt

Chapter19UV-visabsorptionspectroscopy1

OutlinePrincipleofUV-visabsorptionAbsorbanceandquantificationInstrumentationApplicationofUV-visabsorption2

UV-visspectrum200～800nmUV-VisspectraVisiblespectrum400～780nm800nmnearinfrared(NIR)200nmfarultravioletlight(VacuumUV)3

Wavelength/nmColorAbsorbedComplement380-435violetyellow-green435-480blueyellow480-490Greenish-blueorange490-560Bluish-greenred500-560greenRed-purple560-580Yellow-greenviolet580-595yellowblue595-650orangeBlue-green650-780redBlue-greenAbsorptionoflightandcolorofmass4

EnergylevelsandmolecularspectrumEnergyofmolecules(internal,movement,electronic,vibrationalandrotational)EiremainsthesameinmostcasesEm=f(T),asafunctionoftemperature,continuousvariationChangeofenergyunderagiventemperature:ΔΕ=ΔΕe+ΔΕv+ΔΕr,quantum5

EnergyTransitionEnergy/eVWavelengthRangeSpectrumΔΕe1-201230～62nmUV-Vis-NIRUV-vis/electronicspectrumΔΕv0.025～150～1μmIRIR/Vibrational-rotationalspectrumΔΕr0.025～0.00450～300μmFarIRFarIR/RotationalspectrumΔΕeΔΕvΔΕrDiagramofenergystates6

AtypicalUV-visabsorptionspectrumIntensityoftheabsorption:AWavelengthwheremaximumabsorptionwasobtained:λmaxMolarabsorptivitymolarabsorptioncoefficient:εandεmaxForquantitativeanalysis,structuralinformation(qualitative)7

EnergytransitionandabsorptionBondelectrontransitions:σ,π,n;ChargetransfertransitionsLigandfieldabsorption8

MolecularOrbitalTheoryElectronsarenotassignedtoindividualbondsbetweenatoms,butaretreatedasmovingundertheinfluenceofthenucleiinthewholemoleculeInthistheory,eachmoleculehasasetofmolecularorbitals,inwhichitisassumedthatthemolecularorbitalwavefunctionψfmaybewrittenasasimpleweightedsumofthenconstituentatomicorbitalsψi,accordingtothefollowingequationLinearCombinationofAtomicOrbitals(LCAO)approximation9

MolecularOrbitalTheorybondingmolecularo