Photometrization and Processing of IR-LD Spectra Reducing Differential Procedure

4 PHOTOMETRIZATION AND PROCESSING OF IR-LD SPECTRA REDUCING DIFFERENTIAL PROCEDURE 

The method was first published by Zbinden [2] on the basis of a personal communication with Tink and Marrinan concerning the IR-LD analysis of extended polymers. Modification of the method for the circular dichroism was developed by Korte [67]. Called common beam spectroscopy (CBS), the application of the method was further expanded by Jordanov and Tsankov for the measurement of the four variations of infrared dichroism linear and circular polarization, and linear and circular beam refraction [68-70]. 

The vast introduction of the more sophisticated Fourier transform infrared (FT-IR) spectrometers for spectral studies made the CBS method senseless in terms of its further application. In the FT-IR analyses, the linearly polarized measurements are conducted by sequential photometrization of a sample for both positions of the polarizer. The linear dichroism is differentially registered by subtraction of the two spectra, which is implanented promptly and easily by the modem sophisticated FT-IR spectrophotometers, equipped with computerized systans. 

The differential spectrum obtained by the subtraction of the perpendicular (IRj) from the parallel (IRp) spectrum consists of both positive (+) and negative (-) peaks. These peaks correspond to bands, which are more intensive for parallel (+) and perpendicnlar (-) polarization. The angle 9 between the corresponding moments of transition and the orientation director n (see Section 1.1) represents the determining factor in this respect. The analytical expression of this dependence is [52]  

FIGURE 1.12 Molecular structure of S-phenyl-4 -cyanothiolbenzoate according to Ivanova [71], and the view along the a, b, and c axes. 

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