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ELECTROMAGNETICSPECTRUM

Wavenumber(cm-1)

Frequency(Hz)

Wavelength(m)

LEARNINGCHECKWhatexperimentprovedlightbehavesasawave?

Whatexperimentprovedlightbehavesasapar6cle?

List5examplesofphenomenainwhichlightinteractswithma;erasawave.

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YOUNGEXPERIMENT(1800)-PROVEDLIGHTISAWAVE

PHOTOELECTRICEFFECT-LIGHTISAPARTICLE1.  Lightincidentonthe

photocathode2.  Electronsliberated3.  Voltageatanode

adjustedtostopcurrent4.  Stoppingvoltage

dependsoncathodesubstrateandradiaZonenergy

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LEARNINGCHECKSupposethatthescreeninthefigurebelowis3.51mfromtheplancontainingtheslitsandthattheslitsare0.200mmapart.Whatisthewavelengthofthethirdbandfromthecenter,locatedat13mmfromthecentralband?

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LEARNINGCHECKList5examplesofphenomenainwhichlightinteractswithma;erasawave.

LEARNINGCHECK

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INTERACTIONSBETWEENLIGHTANDMATTER

LIGHTASAWAVE•  DiffracZon

•  RefracZon

•  Transmission

•  ReflecZon

•  Sca`ering

•  PolarizaZon

LIGHTASAPARTICLE•  Photoelectriceffect

•  AbsorpZon

•  Emission

•  Sca`ering

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ABSORPTION

ABSORPTION

CompareatomicandmolecularabsorpZon?WhydoesatomicabsorpZonoccuratdiscretewavelengthswhilemolecularabsorpZonoccurinbroadpeaks?

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EMISSION

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LUMINESCENCE

JABLONSKIDIAGRAM

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JABLONSKIDIAGRAMTRANSITIONSElectronicexcita6on-promo6onofanelectrontoanexcitedstate(electronic,vibra6onal,rota6onal).S0àS1

Nonradia6vedecay(vibra6onalrelaxa6on)-vibra6onalenergytransferredtoothermoleculesthroughcollisions.Veryfast.ExcitedstateàS1groundvibra6onalstate

Fluorescence-emissionofphotontoreturntoS0.S1àS0+hν

Internalconversion-radia6onlesstransi6ontoanextremelyvibra6onallyexcitedstateofS0withoutachangeinenergy.S1àS0

Intersystemcrossing-radia6onlesstransi6onfromS1toT1withnochangeinenergy.Changeofelectronspin.S1àT1

Phosphorescence-emissionofphotontoreturntoS0.T1àS0+hν

SCATTERING

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Phenomena TimescaleTransmission 10-14-10-15sNonradiaZvedecay 10-15sElectronictransiZons 10-8sfluorescence 10-5sphosphorescence 10-5to100’ss

TIMESCALESOFTHEFOLLOWINGTRANSITIONS.

BASEDONTHESEOBSERVATIONS,CANYOUPREDICTWHICHTRANSITIONSMIGHTBEMORELIKELYTOOCCUR(ANDTHUSMORECOMMON)?

BEER’SLAWCHEM314

SKOOGNHOLLERCH13

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•  StateandapplyBeer’slaw•  ApplyBeer’slawtoavarietyofusefulsituaZons•  IdenZfycondiZonsunderwhichBeer’slawisnot

linear•  TroubleshootabsorpZonexperimentsandsuggest

waystoregainlinearityinBeer’slaw.•  DeriveBeer’sLawequaZon

OBJECTIVES

ASIMPLEABSORPTIONEXPERIMENT

T=transmissionP0=incidentpowerP=transmi`edpowerA=absorbanceε=molarabsorpZvityb=pathlengthC=analyteconcentraZon

Beer’sLaw

2.85 2.0 1.0 0.5 0.25 0.1 0.01 0.001ConcentraZonrelaZvetomixingdirecZons

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300 400 500 600 700 8000.0

0.5

1.0

1.5

2.0

Abs

orba

nce

(arb

.)

wavelength (nm)

WhatcolordoestheKool-aidabsorb?

Red#40

3

E1JablonskiDiagram

E2

1023

102

Energy

e-

e-

495.2nm

WHY DOES KOOL-AID APPEAR RED?

h`p://img.photobucket.com/albums/v645/fadeout95/roygbiv.gifh`p://roygbivcolors7.files.wordpress.com/2013/01/complementry-color-wheel-copy2.jpg

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0.0 0.1 0.2 0.3 0.4 0.50.0

0.2

0.4

0.6

0.8

1.0

Abs

orba

nce

(arb

)

[Kool-aid]

A=1.9 [Kool-aid]r2=0.97

0.0 0.1 0.2 0.3 0.4 0.50.0

0.2

0.4

0.6

0.8

1.0

Abs

orba

nce

(arb

)

[Kool-aid]

A=ε b[Kool-aid]b=pathlength

y=mx+b

ε molarabsorbZvity

BEER’SLAW:RELATINGANALYTECONCENTRATIONANDABSORBANCE

APPLICATIONOFBEER’SLAWTOMIXTURES

SpectraofmixturescanbeassumedtogeneratealinearcombinaZonoftheindividualcomponentspectra

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M ML

ML2

1.  SoluZonfactors2.  Non-monochromaZclight3.  Notanalyzingatlmax4.  Straylight5.  Mismatchedcuve`es6.  Instrumentnoise

Toomuchortooli`leabsorpZon

SOURCESOFNONLINEARITYOFBEER’SLAW

0.0 0.5 1.0 1.5 2.0 2.5 3.00.0

0.5

1.0

1.5

2.0

2.5

3.0

Abs

orba

nce

(arb

)

[Kool-aid]

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HighanalyteconcentraZons(>0.01M)

HighelectrolyteconcentraZons

RefracZveindexofmediumReacZonswithinthesoluZonHInóH++In-

P0 P

IncidentLight

EmergentLight

Red40

Red40

Red40

Red40

Red40

Red40

Red40

Red40

Red40

Na+ Cl-

Na+

Cl-

Na+ Cl-Na+

Cl-

Na+ Cl-Na+ Cl-

Na+ Cl- Na+ Cl-Na+ Cl-

Na+Cl-

Na+

Cl- Na+Cl-

Na+

Cl-

Na+ Cl-Na+

Cl-

1.SOLUTIONFACTORS

300 400 500 600 700 8000.0

0.5

1.0

1.5

2.0

Abs

orba

nce

(arb

.)

wavelength (nm)

ReacZonswithinthesoluZonHInóH++In-

1.SOLUTIONFACTORS

AbsorpZonprimarilyby

In-

AbsorpZonprimarilyby

HIn

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λ’andλ”aredifferentwavelengths

2.NONMONOCHROMATICSOURCE

300 400 500 600 700 8000.0

0.5

1.0

1.5

2.0

Abs

orba

nce

(arb

.)

wavelength (nm)

ε’ ε’’

3.NOTMEASURINGATLAMDAMAX

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WideslitsallowMorelight(higherthroughput)Moreλ(largerbandwidth)

Monoslitwidthdeterminesspreadofλincidentonsample(bandwidth)

Imageincidentonmonoexitplane

Nosuchthingasafreelunch

EFFECTOFSLITWIDTHS

Whatslitwidthshouldyouchoose?

EFFECTOFSLITWIDTHS

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EFFECTOFSLITWIDTHS

4.STRAYLIGHT

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4.STRAYLIGHT

Differencesin:•  Pathlength•  OpZcalcharacterisZcs

MostlikelytoaffectcalibraZoncurveinterceptSoluZon:Doublebeam:Usematchedcuve`esSinglebeam;Usethesamecuve`e

5.MISMATCHEDCUVETTES

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LEARNINGCHECKListanddescribe4typesofinstrumentalerror

ASIMPLEABSORPTIONEXPERIMENT

Componentsofanabsorp6onexperiment:

1.   0%Tmeasurement(adjustment)

2.   100%Tmeasurement

3.   SampleTmeasurement

Uncertaintyassociatedwithmeasurementistheaggregateofuncertaintyineachstep

UncertaintyassociatedwitherrormeasurementdependsonT

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6.INSTRUMENTALNOISEINTRANSMISSIONMEASUREMENTS

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6.INSTRUMENTALNOISEINTRANSMISSIONMEASUREMENTS

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0.0 0.5 1.0 1.5 2.0 2.5 3.00.0

0.5

1.0

1.5

2.0

2.5

3.0

Abs

orba

nce

(arb

)

[Kool-aid]

LINEARRANGEOFBEER’SLAW

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DERIVATIONOFBEER’SLAWT=transmissionP0=incidentpowerP=transmi`edpowerA=absorbanceε=molarabsorpZvityb=pathlengthC=analyteconcentraZon

LOOKINGAHEADThursday(Jan28)-Beer’sLaw(Ch13,lookthroughderiva6ononwebsite)

ProjectOverview(DueFeb15)FirstdayofConsumerCharacteriza6onProjectExperiment1:MetalsAnalysisDue:Prelab1,Experiment1

Goalsforlabtoday:disassembleyourproject,usehandheldXRF

Monday(Feb1)-Instrumentcomponents(Ch7)

StandardAddi6onDue

Tuesday(Feb2)-Experiment1Metals

Thursday(Feb4)-Experiment1Metals

Prelab2,Experiment1Due