Molecular spectroscopy- pamme

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Where are UV/IR in electromagnetic spectrum in comparison? Their energies, their wavelengths.
UV Vis, shorter wavelength in electromagnetic spectrum, higher energy. IR longer wavelength lower energy.
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Put energy levels in order of size smallest to largest.
rotational levels<Vibrational levels<electronic levels.
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How does UV Vis spectroscopy work?
absorption of UV light, excitation of outer e-, restricted to certain functional groups chromophores.
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equation for transmission and absorption
Transmission = p/p0 (light going out/light going in) Absorption= = log(1/T) or log(100/T%)
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beer Lambert law with units.
A =E(Lmol-1cm-1) *C(molL-1)*B(cm)
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where is beer Lambert law flawed
-chemical and instrumental factors:changes in equilibria, stray light, fluorescence, deviations at high conc(electrostatic attraction)
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Instrumentation for UV Vis
200-800nm light source- wavelength selection-sample holder-light detector-signal processing
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light sources for UVVIs
tungsten lamp, deuterium lamp
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monochromator for UV vis
-disperses light into component wavelengths, selects a narrow band to go to sample. -entrence grit provides narrow optical image- creating splits/disperces light. -exit slit only allows narrow wavelength-wavelength scanning done by moving grate.
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UV vis sample holders
glass, plastic, quartz, transparent and pass radiation.
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name 4 uv vis detectors
-single output detector: PMTphotomultipliertube, PDphotodiode. -multichannel detector- PDAPhotodiodearray CCDchargedcouplingdevice.
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PMT
-photons hit cathode, cathode emits e- acceleration to diode, every time they hit more produce +sensitive+fast-light damages the detector -requires cooling.
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PD
-imcoming photons create electron hole pair, holes move to anode electrons move to cathode. junction acts as capacitor with charge stored. +fast +cheap-less sensitive - the more radiation hits the less charge stored.
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PDA
many silicon photodiodes on one chip. each diode has storage capacitor and switch. individual diodes are scanned, measures all elements simoultaniously. +whole spectrum +good for HPLC
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CCD
-array of photo capacitors, light absorb a valence hole is made e-storred under electrode, hole migrates attaches to e and stored as charge. +very sensitive +good for low light
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IR instrumentation
780nm-1mm IR light source-interferometer-sample holder - detector - computer Fourier transformer.
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IR light sources
Nernst glower, Globar, Nichrome wire
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pyroelectric transducer
dielectric substance with temp dependent polarization, temp sensitive capacitor, IR changes charge distribution which gives electrical signals
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photo conducting transducer
thin film of semiconducting material, absorption of ir raises e- to conduct e- which decreases the electrical resistance.
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thermal transducers
absorption of IR, temp raise, change in voltage/resistance.
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3 detectors for IR
pyroelectric transducers, photoconducting transducers, thermal transducers.
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what does an interferometer do
modulates froquency from IR source to a Time domain signal
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what does a computer Fourier do
converts time domain into a spectrum.
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how does an interferometer work
light hits beam splitter, 50% to each mirror, one mirror moves one is stationary. after reflection beam splitter recombines the light, led to sample. recombined light interferes with each other, in phase or outofphase.
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gas sample prep for IR
cylindrical cell, walls must not interfere with IR
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liquid sample prep for IR
BaF2 ZnSe between two salt disks, very picky solvents.
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solid sample prep for IR
pelleting into KBr disks, Mulls-grind sample with oil nujol between salt plates.
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ATR tools.
light introduced. at critical angle, toil reflection evanescent wave at surface. spectrum is recorded from the sample interaction with evervescant wave.
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spectrum comparison from UV to IR
UV- quantativa analyses, easier faster, samples easier to prep, cheaper. IR- narrower peaks, yields more info, solid liquids and gases.
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explain phosphorescence.
excited triplet state loses energy via collisions from solvent, intersystem crossing with light emission, finally returns to lowest vibrational energy level.
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explain fluorescence.
250-450nm from s1-s0 not involving spin change, absorbs. the light, causes an emission of light, finite reaction.
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Fluorescence instrumentation
light source->excitation monochromator ->sample coveter ^emission monochromator ^detectro.
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effects on fluorescence.
temp effects due to deactivation of excited states by collisions of solvent. pHH+ interacting with fluorophares is bad, has dramatic effect on results.
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what is the inner filter effect.
measurement artifact, detected fluorescence decreases as absorption increases, cannot penetrate deep enough into sample to detect.
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what is photobleaching
degradation of fluorophore over time due to photon induced chemical damage.
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light sources fluorescence
Hg arc lamp, Xenon arc lamp
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sample cell
plastic, glass, quartz
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detectors for Fluorescence
-single output detector: PMTphotomultipliertube, PDphotodiode. -multichannel detector- PDAPhotodiodearray CCDchargedcouplingdevice.
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Other cards in this set

Card 2

Front

Put energy levels in order of size smallest to largest.

Back

rotational levels<Vibrational levels<electronic levels.

Card 3

Front

How does UV Vis spectroscopy work?

Back

Preview of the front of card 3

Card 4

Front

equation for transmission and absorption

Back

Preview of the front of card 4

Card 5

Front

beer Lambert law with units.

Back

Preview of the front of card 5
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