VibrationalSpectroscopy-NUIGalwayNationalUniversityof振动光谱-高威国立大学

VibrationalSpectroscopy-NUIGalwayNationalUniversityof振动光谱-高威国立大学

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时间:2019-08-21

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1、VibrationalSpectroscopyIRSpectroscopy(ofvariousforms,e.g.RAIRS,ATR)ElectronEnergyLossSpectroscopy(EELS)IRSpectroscopyTransmissionIRSpectroscopy:studieswherelargesurfaceareapermitshighconcentrationofadsorbedspecies.DiffuseReflectanceIRSpectroscopy(DRIFTS):diffu

2、selyscatteredIRcollected,refocusedandanalysed.Employedwithhighsurfaceareasamplesnotsufficientlytransparenttobestudiedintransmission.Reflection-AbsorptionIRSpectroscopy(RAIRS):IRspecularlyreflectedfromfrontfaceofahighly-reflectivesample,suchasametalsinglecrysta

3、lsurface.MultipleInternalReflectionSpectroscopy(MIR):IRpassedthroughIRtransmittingsampleandundergoestotalinternalreflection.IRradiationmaybeabsorbedbyspeciesadsorbedonthesolidsurface-alternativenameofAttenuatedTotalReflection(ATR).RAIRSBecausesensitivityindete

4、ctingsub-monolayercoveragescanbeproblematicinRAIRS,usegrazingincidencegeometryRAIRSsurfaceselectionruleonlythosevibrationalmodeswhichgiverisetoanoscillatingdipoleperpendicular(normal)tothesurfaceareIRactiveandgiverisetoanobservableabsorptionband.Surfaceselecti

5、onruleVibrationofapolarmoleculeorientedparalleltothesubstratesurfaceinducesanimagechargeinthesurfacethatcancelsoutthedipole,whereasitisenhancedforvibrationsperpendiculartothesurface(seep.80Attard&Barnes)RAIRSexamplesn(N-O)spectraobtainedfromaPtsurfacesubjected

6、toafixedexposureofNOatvarioustemperatures Note-thesurfacecoverageofadsorbedNOmoleculesdecreasesasthetemperatureisraisedandlittleNOremainsadsorbedattemperaturesof450Kandabove.HCN(a)0.15LHCNat100K TheHCNmoleculesareweaklycoordinatedtothesurfaceinalinearend-onf

7、ashionviathenitrogen;then(H-CN)modeisseenat3302cm-1butthen(C-N)modeistooweaktobeseenandthed(HCN)modeexpectedatca.850cm-1isforbiddenbythesurfaceselectionrule.Theovertoneofthebendingmode,2d(HCN),ishoweverallowedandisevidentatca.1580cm-1. (b)1.50LHCNat100K High

8、erexposuresleadtothephysisorptionofHCNmoleculesintoasecondlayer.ThesemoleculesareinclinedtothesurfacenormalandtheHCNbendingmode(~820cm-1)ofthesesecondlayermoleculesisnolongersymmet

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