INTENSITY-MODULATED PHOTOCURRENT SPECTROSCOPY - RECONCILIATION OF PHENOMENOLOGICAL ANALYSIS WITH MULTISTEP ELECTRON-TRANSFER MECHANISMS

The theoretical framework of intensity-modulated photocurrent spectros copy (IMPS) is extended to photoelectrode processes involving surface- bound intermediates, and the effects of charged intermediates on the s teady state and periodic components of the potential drop across the s emiconductor/electrolyte interface are analysed. The steady state conc entration of charged intermediates alters the band bending and introdu ces a light intensity dependence into the normalised IMPS response. At the same time, light-induced modulation of the concentration of the i ntermediate generates a periodic perturbation of the band bending and consequently of the surface recombination rate. The analysis also take s into account the charging current associated with the periodic compo nent of the photoinduced band bending. It is shown that the experiment al IMPS response can still be analysed using the phenomenological appr oach developed for one-step charge transfer reactions, and the relatio nships between the phenomenological and real rate constants are derive d. Diagnostic criteria for different mechanisms are outlined. (C) 1997 Elsevier Science S.A.