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ID:41295424
大小:312.50 KB
页数:13页
时间:2019-08-21
《VibrationalSpectroscopy-NUIGalwayNationalUniversityof振动光谱-高威国立大学》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
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、toafixedexposureofNOatvarioustemperaturesNote-thesurfacecoverageofadsorbedNOmoleculesdecreasesasthetemperatureisraisedandlittleNOremainsadsorbedattemperaturesof450Kandabove.HCN(a)0.15LHCNat100KTheHCNmoleculesareweaklycoordinatedtothesurfaceinalinearend-onf
7、ashionviathenitrogen;then(H-CN)modeisseenat3302cm-1butthen(C-N)modeistooweaktobeseenandthed(HCN)modeexpectedatca.850cm-1isforbiddenbythesurfaceselectionrule.Theovertoneofthebendingmode,2d(HCN),ishoweverallowedandisevidentatca.1580cm-1.(b)1.50LHCNat100KHigh
8、erexposuresleadtothephysisorptionofHCNmoleculesintoasecondlayer.ThesemoleculesareinclinedtothesurfacenormalandtheHCNbendingmode(~820cm-1)ofthesesecondlayermoleculesisnolongersymmet
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