IRRAS multiple reflection

Thus, in the case of weakly reflecting metal snbstrates, the maximnm intensity of the IRRAS spectmm can be achieved with one reflection, whereas in the case of strongly reflecting metals, the optimum number of reflections, Aopt, should be calculated with Eqs. (2.2) or (2.3), depending on the type of spectrometer used. The optimum angles of incidence are 80-85° and 75°-80°, respectively, for single and multiple reflection. In addition, surface sensitivity of the method can essentially be enhanced by nsing the immersion medium technique (Section 2.5.2). 

In the case of transparent substrates, the sensitivity may be significantly increased with the BML-IRRAS technique (Section 2.3.3) or simply by placing a flat mirror under the substrate while the IRbeam is incident on the other side [16]. The problem that can be met when measuring the IRRAS spectra of films on transparent substrates is interference fringes, which arise due to multiple reflections of the IR beam inside the substrate. To eliminate multiple reflections of the beam and to achieve the... 

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) Reflection-absorption infrared spectroscopy (RAIRS) (also known as infrared reflection absorption spectroscopy, IRAS or IRRAS) Multiple Internal reflection spectroscopy (MIR)... 

Considering multiple reflections at front and back surfaces, the irra-diance of unpolarized light transmitted at normal incidence (0j = 0) through a plate of thickness, h, is determined from a geometrical progression and is given (4) by... 

Very thin films (monolayer or multilayer) can be studied by IR spectroscopy, provided that the IR beam crosses a reasonably large fraction of the monolayer this can be done by (i) grazing-angle techniques (whereby the IR beam angles of incidence and reflection are of the order of 1° to 3°) or (ii) multiple internal reflections of the IRbeam inside the monolayer (infrared reflectance and absorbance spectroscopy (IRRAS). Fig. 11.19 shows the chemical structure of an analyte (Fullerene-fcz s-[ethylthio-tetrakis(3,4-dibutyT2-thiophene-5-ethenyl)-5-bromo-3,4-dibutyl-2-thiophene] malonate),... 

Although the optimum conditions for a number of simple systems are known (e.g., for ultrathin films on metals reflection-absorption (IRRAS) at grazing angles of incidence is commonly used, and for ultrathin films on transparent substrates, multiple internal reflection (MIR) is most suitable in many cases), the spectral contrast can be further enhanced by employing additional special technical approaches. 

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