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FT-IR Instrument

FT-IR Instrument. Components. Source Michelson Interferometer Sample Detector. Sources. Black body radiators Inert solids resistively heated to 1500-2200 K Max radiation between 5000-5900 cm -1 (2-1.7 m m), falls off to about 1 % max at 670 cm -1 (15 m m)

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FT-IR Instrument

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  1. FT-IR Instrument

  2. Components • Source • Michelson Interferometer • Sample • Detector

  3. Sources • Black body radiators • Inert solids resistively heated to 1500-2200 K • Max radiation between 5000-5900 cm-1 (2-1.7 mm), falls off to about 1 % max at 670 cm-1 (15 mm) • Nernst Glower – cylinder made of rear earth elements • Globar- SiC rod • CO2 laser • Hg arc (Far IR), Tungsten filament (Near IR)

  4. Michaelson Interferometer • 1014 Hz is too fast for P to be directly measured as a function of time • Can not measure the FID signal directly • Interferometer creates a replicate interference pattern at a frequency that is a factor of 1010 times slower • 104-105 Hz can be measured electronically • f = (2vm/c)n = 10-10n, vm = 1.5 cm/s

  5. Michaelson Interferometer • Beam splitter • Stationary mirror • Moving mirror at constant velocity • Motor driven Micrometer screw • He/Ne laser; sampling interval, control mirror velocity

  6. Stationary mirror HeNe laser Beam Splitter Source Moving mirror PMT Sample Detector

  7. Sample • Sample holder must be transparent to IR- salts • Liquids • Salt Plates • Neat, 1 drop • Samples dissolved in volatile solvents- 0.1-10% • Solids • KBr pellets • Mulling (dispersions) • Quantitative analysis-sealed cell with NaCl/NaBr/KBr windows

  8. Detector • Transducers • The heating effect of radiation • Thermal transducer- black body, small, very low heat capacity- DT=10-3 K, housed in vacuum, signal is chopped • Thermocouples • Two junctions of dissimilar metals, An and Bi • One is IR detector, one is reference detector • Potential difference that develops in proportional to DT; detection of DTs of 10-6 K is possible

  9. FT-IR detectors • Pyroelectric tranducers

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