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In-class Questions: Infrared Spectroscopy

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    106252

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    Background information

    1. Can infrared spectra be recorded in air? If so, what does this say about the major constituents of air?
    2. Why don’t the major constituents of air absorb infrared radiation? It might be worth noting that a molecule such as hydrogen chloride (HCl) does absorb infrared light.
    3. Describe the vibrations of carbon dioxide (CO2) and determine which ones absorb infrared radiation.

    Specialized techniques

    1. One technique is called non-dispersive infrared (NDIR) spectroscopy. NDIR is usually used to measure a single constituent of an air sample. Think what the name implies and consider how such an instrument might be designed.

    Fourier-transform Infrared Spectroscopy

    1. Consider the light path for a Michelson interferometer and plot the intensity of radiation at the sample versus the position of the moveable mirror for monochromatic radiation of wavelength x, 2x or 4x.

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    1. What are the advantages of FT-IR spectrophotometers over conventional IR spectrophotometers that use a monochromator?

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