215 zyxwvutsrq J. Electroanal. Chem., 266 (1989) 215-225 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP The mirage effect under controlled current conditions Maristella Fracastoro-Decker and Franc0 Decker Institute de Fisica, Unicamp, Campinas, S.P. (Brazil) (Received 6 December 1988; in revised form 17 February 1989) ABSTRACT The deflection of a laser beam parallel to a planar electrode surface, or mirage effect, has been described by means of a mathematical model. The experimental results of ac and transient photoelectro- chemical experiments are shown to agree well with the predictions of this model. From the best fit of the data the following parameters are deduced: the thermal and ionic diffusivity of the electrolyte and the thermal power dissipated at the electrochemical interface. INTRODUCTION zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Considerable interest in the mirage effect is arising among electrochemists for several reasons. First, because it is a recent [l], contactless, thermo-optical spectro- scopic technique, ideally suitable for “ in-situ” studies of the electrode/ electrolyte interface. For this reason it has already found application in semiconductor photo- electrochemistry [2-61 and in spectroelectrochemistry [7,8]. Second, because it is a refractometric technique, extremely sensitive to concentration gradients in an elec- trolyte, it has been used to map the concentration profile near an electrode [9] and to detect diffusion phenomena during cyclic or transient electrochemical reactions zyxwvutsr 13,101. However, although several authors have supplied the theoretical framework and experimental verification to establish the mirage effect as a quantitative thermo-optical technique [ll-131, an analogous framework is missing for the mirage effect in electrochemistry. In two previous short notes we reported the results of the mirage effect with modulated current experiments [14,15]. In the present paper, we analyse the general model that describes such modulation experiments, and we extend it to describe the time response in transient experiments. We have confined our treatment to the case of controlled current experiments because this leads to well-defined concentration profiles [16,17] and because this model is applicable to 0022-0728/89/$03.50 0 1989 Elsevier Sequoia S.A.