Optical SNIFTIRS

The technique used to acquire the data in this paper was SNIFTIRS. A schematic diagram of the required apparatus is shown in Figure 5, and has been described in detail elsewhere. The FTIR spectrometer used was a vacuum bench Bruker IBM Model IR/98, modified so that the optical beam was brought upwards through the sample compartment and made to reflect from the bottom of the horizontal mercury surface. The methods used herein are adapted from a configuration that has been used by Bewick and co-workers (21) at Southampton. 

The infrared-electrochemical cell, originally designed by Bewick and his coworkers, was partly modified to introduce an electrode from the upper part of the cell. The front side of the cell is attached with a CaFg optical window, and the backside with a glass syringe which pushes the electrode against the window. The Fourier transform infrared measurements were conducted at 0 °C for Cu electrodes and at ambient temperature for Ni and Fe electrodes by JIR-6000 (Nihon Densi, Co. Ltd.) externally equipped with an MCT (mercury-cadmium-telluride) detector. Infrared spectra were acquired by the subtraction of two spectra reflected from the electrode at different potentials (SNIFTIRS). The other details were described previously. [9]... 

Fig. 10.8 Thin-layer electrochemical cell used in SNIFTIR studies and reflection optics (a) Teflon cap (b) N2 inlet (c) glass tube (d) Teflon cell body (e) port for reference electrode (f) ceramic tube (g) Pt wire counter electrode (h) single crystal working electrode (i) hemispherical ZnSe window (k) focal plane for reflection optics (m) instrument focal plane and (n) folding mirrors (From reference 16, with permission.)...

Fig. 9.22 An illustration of the SNIFTIRS decoupling procedure. (A) Spectrum calculated for the slab of 5.2x10 ° mol cm of pyridine molecules evenly distributed within the thin cavity between the optical window and the electrode.

The experimental aspects of the performance of in situ FTIR measurements are described in Refs. 33 and 34. Figure 2 shows a typical layout of cells for an in situ external reflectance mode (e.g., SNIFTIRS type measurements) and internal reflectance modes, multiple internal reflectance, ATR, and single internal reflectance mode. " The use of the ATR mode requires crystals, which have a high refractive index (> 2). The common materials that have such a high refractive index and are transparent to the IR in the 500-4000 cm range, which is the most useful optical window for the characterization of functional groups, are KRS-5, ZnSe and germanium (R.I. = 2.37, 2.4 and 4, respectively). The use of the ATR mode requires the facilities of the metal film deposition under UHV. 

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