Chapter 25 - Chapter 25 Instruments for Optical...

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Chapter 25 Instruments for Optical Spectroscopy INSTRUMENT COMPONENTS Most spectroscopic instruments in the UV/visible and IR regions are made up of five components, (1) a stable source of radiant energy; (2) a wavelength selector that isolates a limited region of the spectrum for measurement; (3) one or more sample containers; (4) a radiation detector, which converts radiant energy to a measurable electrical signal; (5) a signal processing and readout unit.
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Optical Materials The cells, windows, lenses, mirrors, and wavelength selecting elements in an optical spectroscopic instrument must transmit radiation in the wavelength region being employed. Ordinary silicate glass is completely adequate for the visible region and has the considerable advantage of low cost. In the UV region, at wavelengths shorter than about 380 nm, glass begins to absorb and fused silica or must be substituted. Also, glass, quartz, and fused silica all absorb in the IR region at wavelengths longer than about 2.5 μ m. Hence, optical elements for IR spectrometry are typically made from halide salts.
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Spectroscopic Sources To be suitable for spectroscopic studies, a source must generate a beam of radiation that is sufficiently powerful for easy detection and measurement. In addition, its output power should be stable for reasonable periods. Spectroscopic sources are of two types: continuum sources , which emit radiation that changes in intensity only slowly as a function of wavelength, and line sources , which emit a limited number of spectral lines. Sources can also be classified as continuous sources, which emit radiation continuously with time, or pulsed sources , which emit radiation in bursts.
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Continuum Sources in the UV/Visible Region An ordinary tungsten filament lamp provides a distribution of wavelengths from 320 to 2500 nm. Generally, these lamps are operated at a temperature of around 2900 K, which produces useful radiation from about 350 to 2200 nm. Tungsten/halogen lamps, also called quartz/halogen lamps, contain a small amount of iodine within the quartz envelope that houses the filament. Quartz allows the filament to be operated at a temperature of about 3500 K, which leads to higher
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This note was uploaded on 05/09/2010 for the course CHEM 3245 taught by Professor Anwara.bhuiyan during the Spring '10 term at Arkansas Tech.

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Chapter 25 - Chapter 25 Instruments for Optical...

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