FT-IR

• Theory
• Vibrational and Rotational Transitions
• Anharmonic Oscillator  Fig. 16-3
• Vibrational Mode
• 3N degrees of freedom   3N-6 defines vibrational modes
• Sources
• Nernst Glower
• Rare earth oxides  Figure 16-4
• Globar
• silicon carbide rod
• Incandescent Wire
• nichrome wire
• Mercury Arc
• far - infrared region
• Tungsten filament
• near - infrared
• Carbon Dioxide Laser
• 900 - 1100 cm-1
• Transducers (detectors)
• Thermal
• detects temp. change
• Thermocouples
• Temp. change
• Photoconducting
• thin film semiconductor
• lead sulfide  most common - used at room temp
• mercury/cadmium telluride  low temp. mid and far IR
• indium antimonide

Instrumentation
 

• Fourier Transform Spectrophotometers
• Michelson Interferometer 7-42 (pg186)
• Key is the moveable mirror
• Beam is split / recombines with intensity variations defining the difference in beam path
• wavelength determines strength of recombination.
• timing of mirror is crucial (laser used)
• interferrograms

•     Table 17-1
•     Chapter 17

Periodic Table

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This document was last modified on Sunday, April 25 1999.