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INTERACTIONSBETWEENLIGHTANDMATTER
LIGHTASAWAVE
LIGHTASAPARTICLE
•
Diffrac<on
•
Photoelectriceffect
•
Refrac<on
•
Absorp<on
•
Transmission
•
Emission
•
Reflec<on
•
ScaDering
•
ScaDering
•
Polariza<on
JABLONSKIDIAGRAM
1
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JABLONSKIDIAGRAMTRANSITIONS
Electronicexcita-on-promo-onofanelectrontoanexcitedstate
(electronic,vibra-onal,rota-onal).S0àS1
Nonradia-vedecay(vibra-onalrelaxa-on)-vibra-onalenergy
transferredtoothermoleculesthroughcollisions.Veryfast.Excited
stateàS1groundvibra-onalstate
Fluorescence-emissionofphotontoreturntoS0.S1àS0+hν
Internalconversion-radia-onlesstransi-ontoanextremely
vibra-onallyexcitedstateofS0withoutachangeinenergy.S1àS0
Intersystemcrossing-radia-onlesstransi-onfromS1toT1withno
changeinenergy.Changeofelectronspin.S1àT1
Phosphorescence-emissionofphotontoreturntoS0.T1àS0+hν
ASIMPLEABSORPTIONEXPERIMENT
T=transmission
P0=incidentpower
P=transmiDedpower
A=absorbance
ε=molarabsorp<vity
b=pathlength
C=analyteconcentra<on
Beer’sLaw
Concentra<onrela<vetomixingdirec<ons
2.85
2.0
1.0
0.5
0.25
0.1
0.01 0.001
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SOURCESOFNONLINEARITYOFBEER’SLAW
1.  Solu<onfactors
2.  Non-monochroma<clight
3.  Notanalyzingatλmax
4.  Straylight
5.  MismatchedcuveDes
6.  Instrumentnoise
ToomuchortooliDleabsorp<on
Absorbance (arb)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
[Kool-aid]
DERIVATIONOFBEER’SLAW
T=transmission
P0=incidentpower
P=transmiDedpower
A=absorbance
ε=molarabsorp<vity
b=pathlength
C=analyteconcentra<on
3
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COMPONENTSOFOPTICAL
INSTRUMENTS
CHEM314
SKOOGNHOLLERCH7
OBJECTIVES
•
•
•
•
•
•
Statethecomponentsandphenomenathatcanbeprobedwith
op<calinstruments.
Recallthemethodsofwavelengthisola<on
Diagram,label,describe,andcompareprism-vsdiffrac<on-based
monochromators
Stateandbeabletoperformcalcula<onsrelatedtomono
performancecharacteris<csandλdispersion.
RecallUV-Visdetectors
Diagram,label,describe,andcomparethefollowingdetectors:
Vacuumphototube,PMT,silicondiode
4
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OPTICALINSTRUMENTATION
Phenomenaprobed
•  Absorp<on
•  Luminescence
•  Emission
•  ScaDering
Components
1.  Stableradia<onsource
2.  Transparentsampleholder
3.  Wavelengthisola<on
4.  Detector
5.  Signalprocessing
BUILDINGASPECTROSCOPICINSTRUMENT
5
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BUILDINGASPECTROSCOPICINSTRUMENT
Components
1.
2.
3.
4.
5.
Stableradia<onsource
Wavelengthisola-on
Transparentsampleholder/op<cs
Detector
Signalprocessing
Thislecturewillfocusoncommoncomponentsof
instrumentsforatomicandmolecularspectroscopies
SOURCES
Whydoesthischartdifferen<atebetweenlineandcon<nuumsources?
Whenwouldyouusealineratherthancon<nuumsource?
6
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OPTICS
SAMPLECUVETTES
Absorbance
Quartzorplas-c?
4
3
Quartz
Plas<c
2
1
0
190
490
790
Wavelength(nm)
1090
7
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BUILDINGASPECTROSCOPICINSTRUMENT
Components
1.
2.
3.
4.
5.
Stableradia<onsource
Wavelengthisola-on
Transparentsampleholder/op<cs
Detector
Signalprocessing
WAVELENGTHSELECTION
8
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MONOCHROMATORBANDWIDTH
Monoslitwidthdetermines
spreadofλincidentonsample
(bandwidth)
Imageincidentonmonoexitplane
Wideslitsallow
Morelight(higherthroughput)
Moreλ(largerbandwidth)
Nosuchthingasafree
lunch
BANDWIDTHMEASUREMENTS
9
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EFFECTIVEBANDWIDTH
EFFECTOFSLITWIDTHONSPECTRALRESOLUTION
10
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FILTERS
FILTERS
11
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MONOCHROMATORS
1.  Entranceslit-providesrectangularop<calimage
2.  Collima<nglensormirror-makeslightbeamsparallel
3.  Dispersiveelement-disperseslightintocomponent
wavelengths
4.  Focusingelement-reformsrectangularop<calimagefocused
onfocalplane
5.  Exitslit-onfocalplane,selectsdesiredbandwidth
MONOCHROMATOR:PRISMSVSGRATINGS
Refrac<on
Reflec<on
Considerthefigures,isλ1orλ2thelongerλandwhy.
λ1>λ2
12
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MONOCHROMATORS:PRISMSVSGRATINGS
WhenmightaprismbebeDerthanadiffrac<onmono?
PRISMSWORKBYREFRACTION
Snell’slaw
Refrac<veindex
13
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BUNSENPRISM
LEARNINGCHECK
Calculatetheangleofdevia-onof350,500and650nmlightasitpassesthrougha
prism.
n350=1.5392
n500=1.5214
n650=1.5145
30°
14
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LEARNINGCHECK
Calculatetheangleofdevia-onof350,500,and650nmlightasitpassesthrougha
prism.
n350=1.5392
n500=1.5214
n650=1.5145
Calculatethedistancebetweenthesethreewavelengthsoflightonanexitplane
placed4cmawayfromtheprism.
REFRACTIVEINDEXOFGLASSASAFUNCTIONOF
WAVELENGTH
15
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OTHERPRISMGEOMETRIES
CornuPrism
LiDrowPrism
REFLECTIONGRATINGMONOCHROMATOR
λ1>λ2
hDps://encrypted-tbn0.gsta<c.com/images?q=tbn:ANd9GcS53If5B18udB7pvW7teXaT3q63kQM1QMWVO1Pbt5R-uV1aXeFg0-T4hL0
16
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ECHELLETTE-DIFFRACTIONLONGEDGE
LEARNINGCHECK
17
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ECHELLEGRATING
LEARNINGCHECK
Calculatetheangleatwhichthe350,500,and650nmlightarereflectedoffthe
surfaceofadiffrac-ongra-ngwith1400groovespermm.Theincidentangleis20
degrees
Compareyourresultswiththeprismcalcula-ons
18
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ECHELLEGRATING
ECHELLEMONOCHROMATOR
19
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MONOCHROMATORPERFORMANCECHARACTERISTICS
1.
Spectralpurity
2.
Dispersionofgra-ng(D)
Reciprocallineardispersion(D-1)
3.
Resolvingpower(R=λ/Δλ)
4.
Effec-vebandwidth(Δλeff)
5.
Lightgatheringpower(F)
Focallength(f)
20
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BUILDINGASPECTROSCOPICINSTRUMENT
Components
1.
2.
3.
4.
5.
Stableradia<onsource
Wavelengthisola<on
Transparentsampleholder/op<cs
Detector
Signalprocessing
IDEALDETECTORS
1.
2.
3.
4.
5.
6.
7.
Highsensi<vity
Highsignaltonoise
Constantdetectorresponseasafunc<onofλ
Fastresponse<me
Nodarkcurrent
Signalpropor<onaltoradiantpower
Rugged,cheap,simple
S=kP+kd
21
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DETECTORS
DETECTORS
Figure7-27
PMT
CdS
GaS
Se/SeO
CdSe
PbS
Siphotodiode
Thermocouple
Golaycell
22
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DETECTORS
Lytle,1974
DETECTORS
23
2/1/16
BARRIER-LAYERPHOTOVOLTAICCELL
VACUUMPHOTOTUBE
1. Photonhitscathode
2. Cathodeemitse-that
travelsthrough
vacuumtotheanode
3. Generatesacurrent
4. Convertedtoa
measureablevoltage
24
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PHOTOMULTIPLIERTUBE(PMT)
PNJUNCTIONS
25
2/1/16
SILICONPHOTODIODE
MULTICHANNELSI-BASEDDETECTORS
Photodiodearray(PDA)
ChargeInjec<onDevice(CID)
ChargeCoupledDevice(CCD)
26
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MULTICHANNELSI-BASEDDETECTORS
Photodiodearray(PDA)
ChargeInjec<onDevice(CID)
ChargeCoupledDevice(CCD)
MULTICHANNELSI-BASEDDETECTORS
Photodiodearray
ChargeInjec<onDevice(CID)
ChargeCoupledDevice(CCD)
27
2/1/16
COMPARINGDETECTORSENSITIVITY
detector
PMT
PDA
CCD
λ
UV
Vis
UV
Vis
UV
Vis
1s
30
122
6000
3300
31
17
10s
6.3
26
671
363
3.1
1.7
100s
1.8
7.3
112
62
0.3
0.2
Harris,Table19-2
LOOKINGAHEAD
Monday(Feb1)-Instrumentcomponents(Ch7)
Tuesday(Feb2)-Experiment1Metals
StandardAddi-onCalcs
Thursday(Feb4)-Experiment1Metals
AtomicSpectroscopy
StandardAddi-onDue
Prelab2,Experiment1Due
28