甲基自由基的光解动力学课件

Photodissociation

dynamicsofthemethylradicalat212.5nm:

EffectofparentinternalexcitationPhotodissociationdynamicsofContentsIntroductionExperimentResultsandDiscussionsConclusionsReferencesContentsIntroductionIntroductionFreeRadicalsImportantinatmospheric,combustionandinterstellarchemistryMuchhardertostudybecausetheyareunstableinnatureDifficulttogenerateIntroductionFreeRadicalsWaystoGenerateRadicalsPhotolysis(Photodissociation)DischargePyrolysis(Heating)ChemicalActivation(Reactions)Thesemethodsareoftenusedinstudiesofradicalspectroscopyanddynamicsstudiedincellexperiments!WaystoGenerateRadicalsPhotoToGenerateRadicalBeams

NozzletipphotolysisDischargenearnozzletipPyrolysisrightbeforeexpansion(PeterChenSource)Advantage:RadicalsarecooleddownintheexpansionDisadvantage:RadicalsarealwaysaccompaniedbytheprecursorsorotherradicalspeciesToGenerateRadicalBeamsNozzWaytogenerateCH3PhotodissociationofCH3IatlowphotolysisenergyprovidesagoodsourceforCH3radicalsCH3I+hvCH3+IInaphotodissociationexperiment,theCH3radicalcanbeseparatedwiththeIatominspace,thereforemakingapureradicalbeamofCH3shouldnotbeverydifficult.WaytogenerateCH3PhotodissocNewtonDiagramforCH3IPhotodissociation

CH3IV(CH3I)u(CH3)u(I)NewtonDiagramforCH3IPhotodEnergyDiagramfortheABandPhotodissociationofCH3IEnergyDiagramfortheABandProductKineticEnergyDistributionat266nm

Parkeretal.ProductKineticEnergyDistribCH3AbsorptionSpectrumnear210nm

CallearandMetcalfeetal.(1-0)BandMebeletal.

CH3AbsorptionSpectrumnear2CH3Potentials

CH3PotentialsExperimentExperimentTheHAtomRydberg“Tagging”Technique

byWelgeetal.

J.Chem.Phys.92,7027(1990)

TheHAtomRydberg“Taggi

212.5nmCH3PhotolysisWavelength:212.5nm212.5nmCH3PhotolysisWavelenResultsandDiscussionsDeterminationofCH3PhotodissociationChannelResultsandDiscussionsDetermiTimeDelay:6.35us

ß=-0.8TimeDelay:6.35usß=-0.8甲基自由基的光解动力学课件CH3+212.5nm—>CH2(X

3B1)+H(2S)(1)CH3+212.5nm—>CH2(ã

1A1)+H(2S)(2)(Eavl=8710cm-1)EnergeticLimit:5800cm-1(Eavl=5563cm-1)CH3+212.5nm—>CH2(X3B1)+H(2S2.Effectofparentinternalexcitation2.Effectofparentinterna)6.50usb)6.65usc)6.80usv2=0v2=0v2=1v2=1a)6.50usb)6.65usc)6.80usEnergeticLimitEnergeticLimitEnergeticLimitEnergeticLimitEnergeticLimitEnergeticLimit:6400cm-1Thevibrationalfrequencyoftheumbrellamode:606cm-1CH3@v2=1EnergeticLimit:6400cm-1The3.AnisotropyParameterDelayTime(μs)6.356.506.656.80β-0.8-0.71smaller6.35μs:afastphotodissociationprocess&μ//C36.50μs:effectoftherotatoinalexcitationofCH36.50,6.80μs:effectofthevibrationalexcitationofCH33.AnisotropyParameterDelProduct3DContourPlot90o0oProduct3D90o0oConclusionsMolecularbeamphotodissociationofhydrocarbonhalides(CH3)canbeusedtoproducepureradicalsourcesforphotodissociationstudiesusingHRTOFmethod.Thisopensanewdirectionforstudiesofphotochemistryofmanyhydrocarbonradicals.CH3photodissociationat212.5nmfromthevibration