Powders, Fibers, and Matte Surfaces

Measurement of the IR spectra of an ultrathin film on a powder sample may be carried out using transmission, diffuse transmittance (DT), diffuse reflectance (DR), or ATR techniques. As mentioned in Section 1.10, calculations to model the IR spectra of ultrathin films on powders under a different set of experimental conditions have not yet been realized. Compared to the stratified systems considered in Sections 2.1-2.6, optimization of the measurements on powders is significantly more complicated. Moreover, this problem has not yet been studied in a systematic fashion. Below current knowledge concerning the optimization of such measurements will be presented, with emphasis on the requirements of the sample. The technical aspects (the production of IR spectra of powders) are discussed in Section 4.2. 

Infrared transmission is the oldest and most highly developed IR spectroscopic method used to study ultrathin films on powdered solids [103, 104]. Buswell 

In the transmission method, the /rt component of radiation that is regularly transmitted through the sample is detected (Fig. 1.22). Measurements of this component do not require any special device—the peUet pressed from the powder is directly positioned in the holder in the sample compartment so as to be in the beam focus. This means that studies of adsorption and catalysis in situ are quite straightforward, based on reactive chambers with a fairly simple optical scheme [111]. Theoretical and practical aspects of the IR transmission spectroscopy of molecules adsorbed on powders have been treated in excellent monographs [108, 109] and will not be repeated here, except to list the basic requirements of the sample. 

OPTIMUM CONDITIONS FOR RECORDING INFRARED SPECTRA OF ULTRATHIN FILMS 

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