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It has been demonstrated that the voltammetric in situ application of electromodulated UV-vis reflectance spectroscopy, electroreflectance (ER) voltammetry, is a powerful tool with which to analyze the electrode reaction of an adsorbed species on an electrode surface. The ER response, which in fact originates from the absorbance change with ac modulation of the electrode potential, was theoretically analyzed and simulated as a function of electrode potential. The results of the theory and simulation were compared to the electrode reaction of Nile Blue A adsorbed on a pyrolytic graphite electrode surface. The resulting ER voltammetry was responsive only to the faradaic processes of Nile Blue A adsorbed on a pyrolytic graphite electrode, and its turnover reaction rate was determined to be in the range of 60-120 5-1. It was revealed through ER measurements that the electronic structure as well as the redox reaction mechanism of the adsorbed Nile Blue A on a graphite electrode were significantly different from those of the native dye. IntroductionThe recent development of spectroelectrochemistry has received a great deal of attention. The combined use of in situ spectroscopic techniques and conventional methods has afforded us a detailed understanding of electrode processes on a molecular level.' A variety of structural and mechanistic information is provided, depending on the method of spectroscopy. Infrared reflection absorption spectroscopy (IRRAS) and Raman scattering (RS) spectroscopy offer information about the structural aspects in the vibrational mode, while ultraviolet-visible (UV-vis) absorption spectroscopy offers similar information in an electronic mode. A body of work on the electrode process using UV-vis absorption has been carried out to measure in situ the spectra of species in the solution phase, among which the optically transparent thin-layer electrode (OTTLE) is most widely utilized.2 Attempts have also been made to measure the spectra of the species in the vicinity of the electrode interface by using the internal reflection method with an optically transparent ele~trode.~The reflection method in UV-vis mode to characterize solid surfaces, often referred as electroreflectance (ER), has developed in solid-state physicse4t5 The method has been widely used in the studies of the electronic band structure of semiconductors. In this method, the reflectance change a t the solid surface due to the perturbation of dielectric properties of the surface is detected as a function of the surface electronic field of the solid.The ER technique has also been applied to metal electrode surfaces combined with conventional electrochemical methods where a change in surface charge causes a change in reflectance. For example, Hinnen and her

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Results of computations carried out on a model in which the samples are contained within cylindrical cavities in a highly conducting block, and in which centre temperatures are measured lead to the following conclusions.(1) The area under a DTA peak is directly proportional to the heat of reaction and mass of the sample and inversely proportional to the thermal conductivity of the material. The area, measured as AT vs. time is independent of the heating rate.(2) The temperature of a DTA peak increases for increasing radius of sample and the variation of sample peak temperature is less than that of the reference material. Hence DTA curves should use sample temperature as abscissa to reduce the influence of differing sample radius used by different experimental designs.The heating rate at the peak of the DTA curve is reduced from the nominal value in samples of large radius. Where the reaction is governed by an equation which is heating rate dependent, then erroneous peak temperatures will be recorded. Further, large radius samples distort the peak shape, and hence small radius samples are important to reduce or eliminate these two effects.(3) The DTA peak reference temperature increases with decreasing sample conductivity and increasing density and specific heat. The peak sample temperature is sensibly independent of the physical properties. The physical properties do, however, influence the peak temperature shift with heating rate leading to erroneous values of activation energies when using techniques outlined by Kissinger (12).The positioning of measuring thermocouples is not so critical in samples of small radius as it is in samples of large radius.(4) Heat loss via the measuring thermocouples causes a reduction in the area under the DTA peak and also lowers the peak temperature.Large heat losses can reduce the actual rate of heating of the centre of the sample even though the rise in block temperature is closely controlled. This fact must be borne in mind when thermocouples are changed, as a change of heat loss will affect the actual rate of heating of the sample.The heat loss may be minimized by the use of thin thermocouple leads, with the limitation that the wires should be conveniently handled when making connections.

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