ELECTRON-TRANSFER KINETICS AND TERNARY EQUILIBRIA OF THE NO2+/NO2/N2O4 SYSTEM BY TRANSIENT ELECTROCHEMISTRY

The reversible redox potential is established for the NO2+/NO2 couple by the cyclic voltammetric (CV) examination of the reduction of the nitronium ion as well as the microscopic reverse oxidation of nitrogen dioxide. The facile association of NO2 and dissociation of N2O4 are specifically included in the electrode kinetics by the successful computer simulation of the cyclic voltammograms at relatively slow and fast CV scan rates. The kinetics of the N2O4 dissociation (k1) and NO2 association (k2) are determined with the aid of single-step chronoamperometry by developing the theoretical working curves based on the CE(mono) mechanism in Scheme II. The strong dependence of the redox potential on the medium is associated with significant NO2+ coordination, as shown by the linear correlation with Gutmann's donor number of the solvent. The heterogeneous rate constant (k(s)) for electron transfer to NO2+ is found to be faster than k(s) for NO+, despite a significantly enhanced value of the intrinsic reorganization energy of NO2+ compared to NO+ for outer-sphere electron transfer based on the Marcus model.