Theoretical sstudy on the Co2+OH2+/Co3+OH2+ electron transfer reactivity

Abstract

This paper presents a contact distance dependence analysis scheme and an abinitio calculation application for the electron transfer (ET) reactivity of Co2+OH2/Co3+OH2 reacting pair. The applicability of these schemes and the corresponding models has been discussed. The contact distance (R CoCo) dependence of the relevant quantities has been analyzed. The results indicate that the activation energy from the accurate PES method agrees well with that from the anharmonic potential method, and they are obviously better than that from the harmonic potential method. The pair distribution function varies from 10−2 to 10−5 along withR CoCo changing from 1.20 to 0.35 nm. The coupling matrix element exponentially decays along with the increase ofR CoCo, and the effective electronic coupling requiresR CoCo smaller than 0.75 nm. In the range from 0.50 to 0.75 nm forR CoCo, the corresponding electronic transmission coefficient falls within 1.0—10−6. The local ET rate also exponentially decays along with the increase ofR CoCo due to the electronic factor. Since the contribution from the pair distribution function to the total ET rate is an inverse measure of that from the electronic factor, the variation of the spherically averaged local ET rate along withR CoCo exhibits a parabola with a maximum at 0.50 nm ofR CoCo. This maximum is close to the overall observed ET rate value. For this mono-hydrated transition metal ionic system, the ET rate generally is about 106 L·mol−1·s−1 in gaseous process. Further, since it is impossible to experimentally determine the structures and their PESs of these hydrated systems, especially for the unstable intermediate species,ab initio calculations can play an effective auxiliary role in discussing the ET reactivities of these kinds of reacting systems.