Transfer of More Than Two Protons

It follows that thus far concerted multiple proton transfer has been demonstrated only for two protons. 

In this contribution we have treated these two transfer mechanisms as limiting cases in a general picture of multiple proton transfer, represented by a model in which the degree of concertedness of the transfer is governed by specific parameters. The basic model concerns double proton transfer in a symmetric potential. 

The parameter controlling the concertedness is the proton-proton correlation represented by a term that is bilinear in the local proton coordinates. The model is combined with a previously developed approach to single proton transfer based on an approximate instanton method. This leads to the recognition of three coupling regimes governing the mechanism of nondassical double proton transfer. 

For the moment these unsolved problems do not seem to seriously hamper our ability to interpret the available data on multiple proton transfer. Most of these data concern concerted transfer under strong-coupling conditions where alternative mechanisms do not contribute. The systems identified as undergoing stepwise transfer under weak-coupling conditions have only been studied at tempera- 

thanks the Ministerio de Education y Ciencia for a Ramon y Research Contract and for Project No. BQU2003-01639. 

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