External versus Internal Reflection

The above geometry (termed external reflection) is the only one usable in practice for bulk metal electrodes (see Fig. 6.2 a) [7j. It has also been used for semiconducting electrodes [19]. Because of the non-negUgible absorbance of electrolytes in the IR, it requires the use of thin-layer cells (1-10 pm), which may be impractical in the presence of Faradaic processes (high series resistance of the electrolyte, non-uniform accessibility of the electrode) or if dynamic information is of interest (large response time of the cell). 

However, a specific character of semiconductors is that they exhibit a wide range of transparency in the IR [20]. Thus, on the high-energy side, the range of transparency is bounded by the forbidden gap (typically lO cm ), and on the low-en- 

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The process of loading zeolites with organometallie complexes always brings to the forefront the question of internal versus external confinement of the metal guest. In this paper we present some experiments based on size exclusion, metal loading and intrazeolite chemistry which in conjunction with FT-FAR-IR, EPR and UV-visible reflectance spectroscopy, critically probe the question of internal versus external location for the case of five representative organometallics,... 

Cation flux rates were assessed for 10 directly in phospholipid vesicles using a dynamic 23Na NMR method. In this procedure, addition of a Dy3+ shift reagent to an aqueous vesicle solution prepared in the presence of Na+ results in an external Na+ signal shifted with respect to internal Na+. With the incorporation of a channel former, the line width broadens, reflecting dynamic exchange between internal and external Na+ through the membrane channel. Consequently, the linewidth varies directly with cation flux and a plot of [channel] versus linewidth permits determi-... 

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