Specac Catalogue 2013

Specac Product Catalogue 2013 | A-Z of IR
A-Z of IR
Infrared spectrum
A plot of Intensity of Infrared radiation vs.
Wavenumber. A spectrum can be interpreted to
determine the molecular structure of the sample
from which it has been obtained, because
different functional groups in a molecule will each
produce a unique feature, or fingerprint, in the
spectrum.
Interferogram
A plot of Infrared detector response vs. Optical
path difference. This is what an FTIR
spectrometer measures, to be Fourier
Transformed to obtain a spectrum.
Interferometer
An optical device causing two beams of light to
travel different distances to produce an optical
path difference. This allows constructive and
destructive interference to occur, and changing
the optical path difference allows the
measurement of an interferogram.
Internal reflection
The effect where electromagnetic radiation
passing through a material reflects off the
surface of the material at the interface with
another medium, which has a lower refractive
index, instead of leaving the material to enter the
new medium. If the angle of incidence is larger
than the critical angle, then none of the light will
be transmitted to the new medium, it will all be
reflected. This phenomenon is called total internal
reflection.
K
KBr pellet
A pellet produced for use in transmission
analysis. This technique is used for powders
and other solids. The sample is ground, then
“diluted” with KBr powder, before being pressed
into a pellet. The pellet is then mounted on a
Specacard before being placed directly in the
Infrared beam for analysis.
Kramers-Kronig Transform
A mathematical calculation performed upon
specular reflectance spectra to eliminate the
effect of variations in the refractive index of the
115
sample. It results in ak-spectrum and an
n-spectrum, which are the true absorbance
spectrum and a plot of Refractive index vs.
Wavenumber respectively.
KRS-5
Trade name for thallium iodide bromide, a
common ATR crystal material (Refractive index
2.38) with Near IR and Mid IR transmission
characteristics.
Kubelka-Munk units
Unit of intensity of diffuse reflected light. The
Kubelka-Munk equation relates this intensity to
the concentration and scattering factor of a
sample. The scattering factoris determined by
the particle size, shape and packing density, but
can be difficult to quantify.
M
Micrometer
A gauge for accurately measuring small
distances, thicknesses etc.
Mid IR
Infrared radiation between 4,000 and 400 cm-1 .
Mull
A Transmission sampling technique. A solid
sample is ground, then dispersed in a mulling
agent (e.g. Nujol). The mull mixture is then
sandwiched between two windows (e.g. KBr) in
an Omni-Cell body before being placed directly in
the Infrared beam.
Mulling agent
(Usually) an oil added to a ground sample in the
preparation of a mull.
N
Near IR
Infrared radiation between 14,000 and 4,000cm-1 .
Nujol
A liquid paraffin used for the preparation of mulls.
Nujol is not always the best mulling agent as it
masks any CH stretch bands that would
otherwise be seen in the sample spectrum.
Cont’d
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