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Indicator Electrodes, Potentiometry, Electrochemistry, Electrode Kinetics, Electrogravimetry, Polarography, Square Wave Voltammetry, Wavelength Selection, Types of Spectroscopy, Detectors, Theory of Molecular Absorption, Absorption by Organic Molecules, Applying UV-vis Spectroscopy are major topics of this course. Main points from these slides are: Continuum Sources, Thermal Radiation, Spectral Distribution Curves of a Tungsten, Incandescent Wire, Tungsten-Halogen Lamps, Gas Discharge Lamps, Hyd
Typology: Slides
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Thermal radiation
(^) (incandescence) –
perfect emitter, perfect absorbertheoretical “Black Body” radiation i.e.,heated solid emits radiation close to the
(^4) therefore need constant
incandescent sourcestemperature for stability when using
law
Spectral Distribution Curves of a Tungsten (Black Body) Lamp
visible region requires high temp.Low temp good for IR, butshifts to shorter wavelengths. At higher temp -> maximum
UV
vis
IR
temperature.All operated at relatively low
emission.Good for IR and give some visible
goes too highOperated in air so will burn up if temp
operates in air, long lifetimeNernst Glower – low power consumption,
changes with usecooled. Long lifetime, but resistanceGlower, requires more power & must beGlobar – more stable than Nernst
Visible Region
(^) sources are:
a)
operated at ~3000Glass enclosed Tungsten (W) filament - normally
(^) o K with inert atmosphere to
emission weaknm, below 350 nm glass envelope absorbs &prevent oxidation. Useful from 350 nm to 2000
b)
high as 3500Tungsten-Halogen lamps - can be operated as
(^) o K. More intense (high flux).
Fingerprints are a problem – also car headlightsalso transmits down to shorter wavelengths).quartz envelope to withstand high temps (whichkeeps filament from burning out. Requireshalide which redeposits W on filament, i.e.,Function of halogen is to form volatile tungsten-
a)
measurementsabsorptionsource for UV- most commonHydrogen Lamp
H (^2) emission is from
Line spectrum fromlimited by jacket180 nm to 370 nm
(^)
PyrexLamp at low pressure in 100 watt Hydrogen
b)
Lamp – sameDeuterium
(^) λ
H distribution as (^2) but with
(3 to 5 times) -higher intensity
D (^2) is a heavier
High pressure Dby collisionsless loss of energyslower so there ismolecule & moves
(^2)
with quartz jacket
d) High Pressure Mercury Lamp – can’t at very high pressures (e.g., 100 atm)with particular electronic transitions evencompletely eliminate bands associated
2 for UV and tungsten for
visible region (switching mid scan)
2 instead of H
2
Lasers (Light Amplification by
Stimulated Emission of Radiation)
states typically using another light sourcestimulated emission and populate upperstart with material that will exhibit
Pumping source used to populate upper states can be flashlamp or another laser
Advantages of lasersOften use prism to select pumping wavelength
angle
Three main approaches:
Block off unwanted radiation –
Disperse radiation & select
Modulate wavelengths at different
frequencies - interferometer
1)
Absorption
(^) – colored glass, colored
film, colored solutions – cheapest way
