| Abstract
| - Double proton transfers in formic acid dimer and formamidine dimerwere studied as prototypes of multipleproton transfer. The potential energy surface (PES) for the doubleproton transfer was studied using ab initioquantum mechanical methods. The solvent effect on the PES was alsoincluded using the Onsager self-consistent reaction field model. In the gas phase, the transitionstate for the double proton transfer in theformic acid dimer complex hasD2h symmetry, but inwater it is changed to aC2v structure, when theHartree−Fock (HF) level of theory is used. When the density functionaltheory is used, the transition state hasD2hsymmetry with and without solvent. However the barrier heightdepends very much on the electron correlation.The double proton transfer occurs synchronously in all the cases.For the formamidine dimer complex, thetransition state has C2vsymmetry in the gas phase, and it changes toCs symmetry in water at the HFlevelof theory. The C2vstructure becomes an intermediate in water, which means that doubleproton transferoccurs asynchronously. In the density functional theory for thegas phase, the transition state hasD2hsymmetry,and it changes to C2vstructure in solution. However the double proton transfer occurssynchronously in bothcases. These results suggest that the correlation is veryimportant to the PES for double proton transfer, notonly in the gas phase but also in solution.
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