Intensity-modulated photocurrent spectroscopy: Reconciliation of phenomenological analysis with multistep electron transfer mechanisms

The theoretical framework of intensity-modulated photocurrent spectroscopy (IMPS) is extended to photoelectrode processes involving surface-bound intermediates, and the effects of charged intermediates on the steady state and periodic components of the potential drop across the semiconductor/electrolyte interface are analysed. The steady state concentration of charged intermediates alters the band bending and introduces a light intensity dependence into the normalised IMPS response. At the same time, light-induced modulation of the concentration of the intermediate generates a periodic perturbation of the band bending and consequently of the surface recombination rate. The analysis also takes into account the charging current associated with the periodic component of the photoinduced band bending. It is shown that the experimental IMPS response can still be analysed using the phenomenological approach developed for one-step charge transfer reactions, and the relationships between the phenomenological and real rate constants are derived. Diagnostic criteria for different mechanisms are outlined. (C) 1997 Elsevier Science S.A.