Theoretical Study On The Electron Transfer Mechanisms Of The Self-Exchange Reaction Between Ferrous And Ferric In Aqueous Solution

Electron transfer reaction of Ferrous-Ferric system in aqueous solution is one of the simplest self-exchange reactions,which is often used as a theoretical model for homogeneous electron transfer reaction.At present,most scholars believe that the electron transfer in Ferrous-Ferric system is carried out according to the direct electron transfer mechanism.Although some researchers have proposed a bridge-assisted super-exchange mechanism,we believe that the nature of the role of water bridges in the reaction process has not been thoroughly studied.In this paper,the mechanism of electron transfer reaction in Ferrous-Ferric system is studied by using effective two state model,orbital interaction and complete active space self-consistent field method.The results show that the electron transfer in Ferrous-Ferric system is based on superexchange mechanism.The following is the arrangement of each chapter.In Chapter 1,we introduce the research background and the work to be carried out.In Chapter 2,we introduce the theory of electron transfer.In Chapter 3,we use the effective two state model and orbital interaction to analyze the nature of water bridge in the electron transfer of Fe(H2O)62+-*Fe(H2O)63+ system.At the same time,based on direct and superexchange electron transfer mechanisms,computational model molecules were established and their electronic coupling,internal reorganization energy and electron transfer rate were calculated by SA-CASSCF.Effective two state model analysis shows that the intermediate state of the bridge orbit will affect the adiabatic wave function and its energy,which is the same as its symmetry,and then affect its electronic eoupling.Orbital interaction analysis shows that bridge orbits can generate a new group of molecular orbits by interacting with metal debris orbits.Compared with the orbital energy levels under the direct electron transfer mechanism,the order of these orbital energy levels has changed,thus changing the corresponding electron coupling.In addition,the calculation results also confirm that the water bridge plays a promotive role in the electron transfer process of Fe(H2O)62+-*Fe(H2O)63+ system.By enhancing the electron coupling,the water bridge has little effect on the recombination energy,making the ratio of superexchange to direct mechanism as high as 226 times.Therefore,we propose that the reaction is carried out in a larger proportion according to the super-exchange mechanism,rather than the direct electron transfer mechanism.In Chapter 4,we study the effect of water bridges on the electron transfer reaction of other species in the Ferrous-Ferric system.We calculated the electron coupling,internal reorganization energy and electron transfer rate of two electron transfer reactions of Fe(H2O)5(OH)+-*Fe(H2O)5(OH)2+ and Fe(H2O)5Cl++*Fe(H2O)5Cl2+ using SA-CASSCF method.Through calculation and theoretical analysis,we find that the participation of water bridge can also promote the electron transfer reaction of other species in Ferrous-Ferric system.Thus,it is also shown that the electron transfer reactions of other species in Ferrous-Ferric system are also carried out according to the super-exchange mechanism.