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TYPESOFERRORSINTHELABORATORY1.Randomerror• Alwayspresent,alldirecHons• OJenlimitsprecisionofmeasurements• QuanHfy:standarddeviaHon2.Systema1c• Affectsallmeasurementsinthesameway-DirecHonand
magnitude• Assignablecause• QuanHfy:bias
3.Gross• Bigoops!• Generallyclear• Outliers?
ErrorFamilyTree
SOURCESOFEXPERIMENTALNOISEChemical• Experimentsareaffectedbyuncontrollable
environmentalcondiHonsaffecHngsystem
Instrumentalnoise• Affectsallcomponentsoftheinstrument
• Observednoiseisacomplexcompositeofallnoise
sources
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SOURCESOFINSTRUMENTALNOISE
1. Thermal/Johnson2. Shotnoise3. Flickernoise4. Environmentalnoise
IMPROVINGS/NSTATISTICS
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LIGHT-MATTERINTERACTIONSCHEM314
• ReviewelectromagneHcradiaHonandEMspectrum• Wave-parHcleduality
• Overviewofwayslightcaninteractwithmaaer• ApplytheseinteracHonstothestudyofchemical
systems• SummarizeexcitaHonandrelaxaHonwithinanatomor
moleculeusingaJablonskidiagram.
OBJECTIVES
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Spectroscopy?InteracHonbetweenlightandmaaer
ELECTROMAGNETICRADIATIONAamplitudepperiod(sec)νFrequency(sec-1;Hz)λWavelength(m-nm)vvelocityofpropagaHonwavenumber(1/λ;cm-1)Ppower(energys-1)Iintensity(Psolidangle-1)
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Whatisthefrequencyandenergyof500nmlight?
WAVELENGTH,FREQUENCY,ANDENERGY
WAVELENGTH,FREQUENCY,ANDENERGY
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ELECTROMAGNETICSPECTRUM
Wavenumber(cm-1)
Frequency(Hz)
Wavelength(m)
λ
ν
89.9x106HzPublicRadio Molecular
vibraHonsCoreelectronejected
NucleartransiHons
ElectronictransiHons
MolecularrotaHons
INTERACTIONSBETWEENLIGHTANDMATTER
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SUPERPOSITIONOFWAVES
INTERACTIONSBETWEENLIGHTANDMATTER
LIGHTASAWAVE• DiffracHon
• RefracHon
• Transmission
• ReflecHon
• Scaaering
• PolarizaHon
LIGHTASAPARTICLE• Photoelectriceffect
• AbsorpHon
• Emission
• Scaaering
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DIFFRACTION-BENDINGOFLIGHTASITPASSEDTHROUGHASLIT
Wavegenerator Wavegenerator
YOUNGEXPERIMENT(1800)-PROVEDLIGHTISAWAVE
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TRANSMISSION-TEMPORARYPOLARIZATIONOFMOLECULES
Atagivenfrequencyi:nirefracHveindexvivelocityofpropagaHoncspeedoflightinavacuum
RefracHveindex:
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DISPERSION-CHANGEINREFRACTIVEINDEXWITHFREQUENCY
Goodforlenses
Goodforprisms
REFRACTION-BENDINGOFLIGHTATINTERFACESOFMEDIA
Lessdense
Moredense
Lightbendstowardnormal
Snell’slaw
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REFLECTION-REFLECTIONOFLIGHTATANINTERFACE
hap://maxgrace.wordpress.com/2010/07/14/the-love-chapter-one-more-Hme/
SCATTERING-CHANGEINMOMENTUMOFEMRADIATIONRayleigh-elasHcscaaeringMie-largeparHclesRaman-inelasHcscaaering
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POLARIZATION-SELECTIONOFASPECIFICORIENTATIONOFEMRAD.
INTERACTIONSBETWEENLIGHTANDMATTER
LIGHTASAWAVE• DiffracHon
• RefracHon
• Transmission
• ReflecHon
• Scaaering
• PolarizaHon
LIGHTASAPARTICLE• Photoelectriceffect
• AbsorpHon
• Emission
• Scaaering
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PHOTOELECTRICEFFECT1. Lightincidentonthe
photocathode2. Electronsliberated3. Voltageatanode
adjustedtostopcurrent4. Stoppingvoltage
dependsoncathodesubstrateandradiaHonenergy
PHOTOELECTRICEFFECT
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ABSORPTION
ABSORPTION
CompareatomicandmolecularabsorpHon?WhydoesatomicabsorpHonoccuratdiscretewavelengthswhilemolecularabsorpHonoccurinbroadpeaks?
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JABLONSKIDIAGRAMTRANSITIONSElectronicexcita1on-promo1onofanelectrontoanexcitedstate(electronic,vibra1onal,rota1onal).S0àS1
Nonradia1vedecay(vibra1onalrelaxa1on)-vibra1onalenergytransferredtoothermoleculesthroughcollisions.Veryfast.ExcitedstateàS1groundvibra1onalstate
Fluorescence-emissionofphotontoreturntoS0.S1àS0+hν
Internalconversion-radia1onlesstransi1ontoanextremelyvibra1onallyexcitedstateofS0withoutachangeinenergy.S1àS0
Intersystemcrossing-radia1onlesstransi1onfromS1toT1withnochangeinenergy.Changeofelectronspin.S1àT1
Phosphorescence-emissionofphotontoreturntoS0.T1àS0+hν
JABLONSKIDIAGRAM
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SCATTERING
Phenomena TimescaleTransmission 10-14-10-15sNonradiaHvedecay 10-15sElectronictransiHons 10-8sfluorescence 10-5sphosphorescence 10-5to100’ss
TIMESCALESOFTHEFOLLOWINGTRANSITIONS.
BASEDONTHESEOBSERVATIONS,CANYOUPREDICTWHICHTRANSITIONSMIGHTBEMORELIKELYTOOCCUR(ANDTHUSMORECOMMON)?
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LOOKINGAHEADTuesday(Jan26)-ProjectOverview(DueFeb15) LastdayforStandardAddi1on(DueFeb1)
Thursday(Jan28)-Beer’sLaw(Ch13,lookthroughderiva1ononwebsite)FirstdayofConsumerCharacteriza1onProjectExperiment1:MetalsAnalysisDue:Prelab1,Experiment1