| Abstract: | The geometries of two reaction systems have been optimized under the constraint of C2ν symmetry, using the UHF/6‐31G method. The potential energy surfaces (PES) of the two systems in different external electric field have been constructed using a linear reaction coordinate. It is concluded that the reorganization energies and electron transfer matrix elements for both systems are almost independent of the external electric field. However, the standard Gibbs energy difference changes remarkably with the change of the external electric field. Hence, the applied electric field leads to the variation of rate constant of electron transfer reaction. The threshold field, where the electron transfer becomes barrier free, is obtained to be 0.0015 a.u. for the anion system 1, and 0.00097 a.u. for the anion system 2. The threshold field for modified system 1, in which the hydrogen atoms linking to benzene rings are replaced by fluorine atom, is 0.0018 a.u. The calculations show that the best way to adjust the threshold field is to adjust the dipole moment of the reaction system by changing the length of the bridge. As the rate constant in field‐free case is taken into account, neither reaction systems could be used as molecular electronic device. But if the bridge consists of three or four HCTDs, the rate constant and threshold field will satisfy the practical demand. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 |
