Variable-temperature studies cell design

More sophisticated OTTLE designs have been proposed. For example, a very successful variable temperature OTTLE cell has been used for many years by Heath at Canberra [108] and Yellowlees at Edinburgh, Fig. 11 [109]. The latter cell has been used in studying the spectroelectrochemistry of a porphyrin-viologen dyad. The first two reductions were viologen based while the second gave rise to a porphyrin anion radical, confirmed by EPR spectroscopy [110, 111]. A similar cell is... 

The variable-temperature cell in which reactive intermediates can be studied at temperatures down to — 130°C (Figure 6.18) is designed with opposed, coaxial working, and Luggin-probe electrodes surrounded by a platinum-coil counter electrode. The cylindrical symmetry provides uniform current and po-... 

Bond and coworkershave developed a small-volume (0.2 ml) variable-temperature EPR spectroelectrochemical cell that enables simultaneous rapid-scan voltammetry and EPR measurements to be made. The performance of this cell is compared to that of a flow-through cell designed by Coles and Compton. The small-volume cell permits cyclic voltammetric studies at variable temperatures but has significantly lower sensitivity compared to the flow-through cell, which is not amenable to low-temperature work. 

The cell designs wc have successfully utilised with uv/vis/nir and epr spectrometers are detailed briefly. The variable temperature control of our cells is an important feature since many redox products are stable only at low temperatures. The range of systems which can be studied speciroclcctrochemically are extensive. This paper considers only redox processes which are... 

In view of the uncertainties inherent in Hammett indicator determinations of surface acidity by visual means, a study was made of the spectral behavior of dyes adsorbed on several silica-alumina catalysts and silica gel (62). The effects of catalyst water content, dye concentration, catalyst composition and pretreatment on the spectra of the adsorbed dyes were examined. The Hammett indicator dyes employed and their corresponding pKA values are summarized in Table II. Reference spectra were determined for the base-form of the dye in iso-octane or methylene chloride solution and for the acid-form in an aqueous sulfuric acid or ethanolic-hydrogen chloride solution. Dyes were adsorbed from isooctane solutions onto thin plates of optically transparent catalysts which were installed in evacuated cells of design similar to that shown in Fig. 4. The catalysts samples were routinely pretreated by calcination in oxygen at 500° to remove any organic contaminants, followed by evacuation at this temperature. To examine the effect of variable water content on the spectra the samples were rehydrated in an atmosphere of wateir vapor for 24 hr after pretreatment and subsequently evacuated at some lower temperature. Dye solutions were introduced through a side arm. These solutions were suitably dilute so that the absorbance due to dissolved dye was either below the limits of detection or, at... 

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