ABSTRACT
B. The Born-Oppenheimer Approximation and Potential
Free-Energy Surfaces ............................................................................................... 695
C. Totally Diabatic Proton Transfer ............................................................................. 696
D. Partially Adiabatic Proton Transfer ......................................................................... 697
E. Totally Adiabatic Proton Transfer ........................................................................... 698
F. General Expressions for the Tunnel Transmission Coefficient
and Transition Probability. The Environmental Medium Dynamics...................... 698
G. Fluctuations of the Interreactant Distance and Gated Proton Transfer .................. 700
H. Free Energy Relations and Kinetic Isotope Effects ................................................ 701
III. Proton Transfer in Hydrogen-Bonded Systems............................................................... 702
A. Hydrogen Bonds with Double-Well Proton Potentials ........................................... 703
B. Excess Aqueous Proton Conductivity and Proton Transfer.................................... 705
1. Proton Hops between Two Water Molecules ................................................... 706
2. Short-Range Proton Transfer via Adjacent Zundel Complexes....................... 706
3. Long-Range Proton Transfer via Remote Zundel Complexes ......................... 707
B. Proton Transfer in Single-Well Proton Potentials................................................... 709
IV. Electron-Coupled Proton Transfer................................................................................... 710
A. Mechanisms of Dynamic and Step-Wise Coupling ................................................ 711
B. A View on Coherent Two-Proton Transfer in Zundel Complexes......................... 714
C. Models and Mechanisms of Electron-Coupled Proton Transfer (ECPT) ............... 715
1. Diabatic States................................................................................................... 716
2. Mechanisms of Transitions and Rate Constants............................................... 718
D. Synchronous Electron and Proton Transfer............................................................. 720
V. Concluding Remarks........................................................................................................ 720
Acknowledgments ........................................................................................................................ 722
References..................................................................................................................................... 722
The ubiquity and importance of proton transfer (PT) as an “elementary” reaction step are equaled
only by those of electron transfer (ET). PT and ET show both close physical and formal analogies,
and important differences. Light particles, with conspicuous quantum mechanical (tunneling)
features at room temperature are transferred between much heavier molecular fragments in both
cases. Both particles are also strongly coupled to the polar or apolar environment (solvent, protein).
The view of vibrationally assisted proton tunneling was introduced early.
