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Chapter III CHN Analysis, FT IR …..
scanning and automatic control of slit, period and gain. These are very often
under the control of a microprocessor. Accessories such as beam condensers,
reflectance units, polarizers and micro-cells can usually be added to extend
versatility or accuracy [5].
3.5 Fourier Transform Infrared Spectroscopy
Multiplex type of instruments employs the mathematical tool of Fourier
Transform [6]. The apparatus of Fourier Transform Infrared (FTIR)
spectrometer is derived from Michelson interferometer, which is shown in
figure (3.4). The main components of the FTIR spectrometers are (1) drive
mechanism, (2) beam splitters and (3) sources and transducers. In figure
(3.5) a parallel beam of radiation is directed from the source to the
interferometer, consisting of a beam splitter (B) and two mirrors (M1 and M2).
It is well known that for coherent and monochromatic radiation the
interference patterns can be obtained.
The constructive or destructive interference is produced depending on
the relative path lengths B to M1 and B to M2. When mirror M2 moves
smoothly towards or away from B, a detector sees radiation of changing
intensity. If white radiation is used, the interference patterns are obtained
which can be transferred back to the original frequency distribution. This can
be achieved by a mathematical process known as Fourier Transform,
nowadays; this process is carried out by a computer or microprocessor of
the spectrometer. Under these conditions, the detector response fluctuates
at a rate, which depends upon the rate of movement of mirror and the
wavelength of radiation. In general, any combination of frequencies with
corresponding amplitudes will produce an interferogram containing all the
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