Effect of the nonideality of the contact between the sample and the reflecting element on the relative intensity of the bands in an MDTIR spectrum

Abstract

The problem of quantitative analysis of MDTIR spectra, associated with the nonideality of the contact between the sample and the reflective element, can in principle be solved also on the basis of the traditional MDTIR spectroscopy, employing solid-state reflecting elements. The idea is to reconstruct the spectrum corresponding to an ideal contact between the sample and the reflecting element from the experimental (obtained with a poor contact) MDTIR spectrum. It is obvious that this procedure is possible only in the case when the laws governing the effect of the nonideality of the contact on the characteristics of the MDTIR spectrum are known. The purpose of this work is to establish these laws for the relative intensity of the absorption bands. We formed the studies on samples of polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC), some of whose characteristics are presented in TabLe I. We used an MII-4 interference microscope to make a quantitative determination of the roughness of the surface of the samples. The IR spectra (MDTIR and transmission) were recorded on a UR-20 spectrophotometer. A serially produced MDTIR attachment to this device with reflecting elements consistng of KRS-5 (10 reflections at an angle of 55 ~ and Ge (28 reflections at an angle of 45 ~ crystals were employed. The same force clamping the samples to the MDTIR element was achieved for all samples in all cases by turning the clamping screws manually as far as they could be turned.* In the case of an ideal contact between the sample and the reflecting element the intensity of the absorption bands in the MDTIR spectrum is given by the following equation [i]: % *In order to evaluate the reproducibility of the contact achieved in this manner between the sample and the reflective element five MDTIR spectra of the control sample were recorded. Before each spectrum was recorded the sample in the cell was recharged. The spread in the values of the peak intensities of the absorption bands in the MDTIR spectra obtained equalled ~2%.