Infrared reflectance spectrum, reduced

Figure 1. Infrared reflectance spectrum of reduced YBa2Cu30y displaying onset of electronic absorption with a maximum near 640 cm.-l...

The measurement of diffuse reflectance effectively involves focusing the infrared source beam onto the surface of a powder sample and using an integrating sphere to collect the scattered infrared radiation.59 The technique requires careful attention to sample preparation, and often one must dilute the analyte with KBr powder to reduce the occurrence of anomalous effects.60 In practice, one obtains the spectrum of the finely ground KBr dispersant, and then ratios this to the spectrum of KBr containing the analyte. The relative reflectance spectrum is converted into Kubelka-Munk units using standard equations,61 thus obtaining a diffuse reflectance spectrum that resembles a conventional IR absorption spectrum. 

Infrared spectroscopy can provide a great deal of information on molecular identity and orientation at the electrode surface [51-53]. Molecular vibrational modes can also be sensitive to the presence of ionic species and variations in electrode potential [51,52]. In situ reflectance measurements in the infrared spectrum engender the same considerations of polarization and incident angles as in UV/visible reflectance. However, since water and other solvents employed in electrochemistry are strong IR absorbers, there is the additional problem of reduced throughput. This problem is alleviated with thin-layer spectroelectro-chemical cells [53]. 

Nonpowdered samples can be studied directly from the sample surface as long as the surface is irregular (granular) and not polished. In some cases, a thin film of KBr powder placed on the surface of the sample may help to improve the final spectrum quality this works well with fibers, fabrics, and paper samples. In this case, the KBr film reduces the incidence of unwanted surface reflections and helps to ensure better coupling between the sample and the infrared beam by promoting penetration beyond the surface. 

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