An Ab Initio Study of Specific Solvent Effects on the Electronic Coupling Element in Electron Transfer Reactions

An ab initio study of specific solvent effects on the electronic coupling element in electron transfer reactions. Specific solvent effects on the electronic coupling element for electron transfer are examined using two model donor–acceptor systems (Zn 2 ϩ and Li 2 ϩ) and several model ''solvent'' species (He, Ne, H 2 O, and NH 3). The effects are evaluated relative to the given donor–acceptor pair without solvent present. The electronic coupling element (H ab) is found to depend strongly on the identity of the intervening solvent, with He atoms decreasing H ab , whereas H 2 O and NH 3 significantly increase H ab. The distance dependence ͑essentially exponential decay͒ is weakly affected by a single intervening solvent atom–molecule. However, when the donor–acceptor distance increases in concert with addition of successively greater numbers of solvent species, the decay with distance of H ab is altered appreciably. Effects due to varying the orientation of molecular solvent are found, somewhat surprisingly, to be quite modest.