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Chapter III CHN Analysis, FT IR …..
Figure: 3.5 Schematic diagram of FTIR spectrometer.
(1) A drive mechanism is important for satisfactory interferograms, which
needs that the speed of the moving mirror should be constant and its
position be known exactly at any instant. The planarity of the mirror
must remain constant during the entire sweep of 10 cm or more.
(2) Beam splitters are constructed of transparent materials with refractive
indices such that approximately 50% of the radiation is transmitted and
50% is reflected. A thin film of germanium or silicon coated on cesium
iodide or bromide, sodium chloride or potassium bromide is employed
for mid infrared region.
(3) The sources of FTIR are usually the same as IR ones. Because of
processing the slow response times, the thermal transducers are not
generally preferred in FTIR; the Triglycine Sulphate transducers are
widely preferred in the mid-frequency range.
The FTIR instrument has many advantages. It has better signal to noise
ratio than other good quality dispersive type instrument. Another important
advantage is that its optics provides a much larger energy throughput (one or
two orders of magnitude) than the dispersive type, where it is limited by the
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