Infrared Linear Dichroism Measured with a Monochromator

DYNAMIC INFRARED LINEAR DICHROISM MEASURED WITH A MONOCHROMATOR 

In Chapter 19 we saw that kinetic processes cannot be studied with a conventional rapid-scanning interferometer when the reaction rate is so fast that the reaction is essentially complete by the time just one or two interferograms have been measured. Instead, very fast reactions must be repeated at each retardation step of a step-scan interferometer. A different but related approach to the measurement of reversible dynamic systems can also be made with step-scan interferometers. In this case, however, very small changes in the state of the sample are introduced by subjecting it to a modulated perturbation of some type. Dynamic information can be obtained when the phase of the induced signal lags behind the phase of the perturbation by several degrees. An example of a reversible modulated process is when a polymer film is subjected to a modulated uniaxial strain, and this measurement is discussed in some detail in the first four sections of this chapter. 

Fourier Transform Infrared Spectrometry, Second Edition, by Peter R. Griffiths and James A. de Haseth Copyright 2007 John Wiley Sons, Inc. 

SAMPLE MODULATION SPECTROMETRY WITH A STEP-SCAN INTERFEROMETER 

The output from the detector preamplifier is also passed into a fourth LIA, D, referenced to the chopper, the output of which is the static absorption spectrum in other words, the conventional single-beam spectrum. Finally, the output of this LIA is input to another dual-phase LIA, E, referenced to the chopper firequency. The phase control of LIA E had been set prior to the experiment in the same way as LIA C. The outputs of LIA E are the in-phase and quadrature absorbance spectra. 

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