Download (4Mb) - Etheses - Saurashtra University

Chapter III CHN Analysis, FT IR …..
dispersive type based on diffraction gratings. Due to the advent of Fourier
Transform technology, the scenario is completely changed. Photometers
based on interference filters also find applications in measuring the
composition of gases and atmospheric contaminants. Before the appearance of
these new instruments, the mid-infrared frequency region of the spectra were
largely used for organic qualitative analysis and structural determination based
on absorption spectrum. Nowadays, the mid-infrared spectroscopy is used for
quantitative analysis for complex samples by both absorption and emission
spectrometry. In addition to this the mid-infrared spectral regions find
applications in microscopic studies of surfaces, analysis of solids by attenuated
total reflectance and diffuse reflectance, photo-acoustic instruments and others
[2].
The infrared region of the electromagnetic spectrum extends from the
red end of the visible spectrum to the microwave region. Infrared spectral
region can be divided into three regions; near-infrared, mid-infrared and far-
infrared. Table (3.2) gives the details of different infrared spectral regions.
Molecular vibrations are falling into basic categories of stretching and bending.
A stretching vibration involves a continuous change in the inter-atomic distance
along the axis of bond between two atoms. However, the bending vibrations
are characterized by a change in the angle between two bonds, which are of
four types, scissoring, rocking, wagging and twisting in the figure (3.2).
Because of the interaction with infrared radiation, portions of the incident
radiation are absorbed at particular wavelengths. The multiplicity of vibrations
occurring simultaneously produces a highly complex absorption spectrum,
which is a unique characteristic of the overall configuration of the atoms as well.
127