NONLINEAR ARRHENIUS BEHAVIOR OF THE RATE CONSTANTS OF SOME ACTIVATION-CONTROLLED REACTIONS OF THE HYDRATED ELECTRON IN THE TEMPERATURE-RANGE 20-200 DEGREES-C

Rate constants for the reaction of e(aq)- with N2O, NO3-, NO2-, phenol, SeO42-, S2O32- and Mn2+ have been measured in the temperature range 20-200-degrees-C by pulse radiolysis. In each case non-linear Arrhenius behaviour of the rate constant has been observed for the activation-controlled part of the overall process of diffusion and reaction. The activation energies (E(a)) decrease with increasing temperature and, except for Mn2+, become negative. The data are interpreted in terms of a model for reversible electron transfer which implies that activation-controlled reactions of e(aq)-, may be reversible. In the case of Mn2+, E(a) first decreases and then increases with increasing temperature. It is suggested that a second channel becomes operative at elevated temperatures for the reaction of e(aq)-, with Mn2+.