Spectroscopy for Analysis of Automobile Emissions

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Spectroscopy for Analysis of Automobile Emissions
Stedman, Univ. of Denver
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Stedmans Work
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Double-Beam Spectrometer
Light is alternated through a reference and
sample cell so you do not have to swap out the
blank and the analyte.
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Insides of a DB Spectrophotometer
Deuterium arc lamp
Halogen lamp
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Lamp Sources

• Tungsten lamp (320-2500 nm)
• Deuterium arc lamp (200-400 nm)
• Hg vapor arc lamp (225 -800)
• Xe gas arc lamp (200-1000 nm)
• Globar (SiC) (1-40 mm)

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Emission Wavelentghs of D2 and W
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How does a Laser Work?
When a photon from E2 hits another E2 it causes
another photon
Molecules put into excited state by a lamp or
electric discharge
Fast Processes
(Greater population of excited state than ground
state)
Laser light is coherent, meaning that all
waves are in phase
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Laser Sources

• Lasers can be operated as constant output
  (continuous wave-CW) or pulsed output
• Solid-state
• NdYAG (1064, 532, 266 nm)
• Ruby laser (694.3 nm)
• Gas lasers
• HeNe (3390, 1150, 633 nm)
• Ar (488.8, 514.6 nm)
• CO2 (10600 nm)
• Dye lasers (virtually any wavelength)

Most reliable lasers
Most powerful lasers
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Monochromators

• A monochromator disperses light into component
  wavelengths and picks a narrow band to pass on to
  sample cell or detector
• The most common is a diffraction grating, which
  is an optical component with a series of lines
  that reflect light
• As light hits the lines, each of the lines
  behaves as an individual light source

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Grating Diagram
Collimates (makes parallel) the light
Focuses the light
?s diffract at different angles
Only 1 ? at a time can make it through the slit