2000 Volume 16 Issue 1 Pages 87-91
A long-path-length spectroelectrochemical technique was developed for investigating the EC mechanism and evaluating the kinetic parameters under a semi-infinite condition. The chronoabsorbances were obtained by a digital simulation method. Simulated results showed that the shapes of A-t curves are markedly dependent upon the relative values of the molar absorptivities of spieces A, B and C. When εA=0, εB/ εC≥5 or εC=0, 0≤εA/εB<0.5, the system absorbance passes through a maximum (Amaxt) interestedly. While εB=0, 0.2≤εA/εC≤1, there appears a minimum (Amint). Either Amaxt or Amint is closely related to the chemical reactions following charge transfer. When there is Amaxt at moment tmax in the A-t curve, increasing the value of the first-order rate constant (k1) causes Amaxt and tmax to decrease; while increasing the diffusion coefficient (DB) for species B causes Amaxt to increase, but tmax to decrease. This opposite effect enables us evaluate k1 and DB both simultaneously and precisely. The elctrooxidation of p-aminophenol in an acid aqua solution was experimentally investigated by a long-path-length spectroelectrochemical technique. The pseudo first-order rate constant and the diffusion coefficient for the electrooxidized intermediate quinone imine were successfully evaluated by this method.