Page 89 - Tandem Techniques
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procedure necessary to correct for these effects differ greatly from the precautions that need to be taken
against fluorescence.
A given substance will give a characteristic Raman spectrum under controlled conditions and the
spectrum can be used to confirm the identity of the substance. An example of the relative absorption
curves for infrared and Raman spectroscopy is shown in Figure 2.14. It is seen that the spectra for the
gasoline's having different octane rating are very similar but, although the IR spectra show minimal
differences between the samples, there are clear and unambiguous differences in the Raman spectra. In
Figure 2.15 spectra are shown that have been taken from aspirin powder by diffuse reflectance infrared
and Raman spectroscopy.
Figure 2.15
IR Diffuse Reflectance and Raman
Spectra of Aspirin Powder
Courtesy of the Perkin Elmer Corporation
It is seen that absorbance and Raman scattering takes place at very similar wavelengths and there is
little to choose between the two spectra for substance identification. However if the sample is in another
form, e.g. as
