Proton jumps and molecular reorientations

We here envisage a more complex type of proton transfer mechanism involving a combination of molecular reorientations and proton jumps. For the classic case of proton transfer from H30 to HjO in a crystalline 

A neutron diffraetion experiment will again sense this type of idealized overlap situation as a nuelear density involving a number of overlapping partially occupied sites. The refined occupations of each fractional site will give some indication of the mechanisms involved. In practice, we are faced with the problem of interpreting an overlap density in terms of some reasonable disordered model involving an overlap of the expected H2O and moieties. This interpretation is then incorporated into an 

The refinement of a single-crystal neutron diffraction data-set collected for the well-known proton conducting compound NH4 /H30  

P -alutnina serves to illustrate this type of procedure. Each apex of the hexagonal-shaped pathways of J -alumina is occupied to 80% by NH4 ions. Following the scheme of the preceding discussion, the difference Fourier syntheses after the inclusion of NH4 ions in the refinement were interpreted in terms of a complicated overlap of HjO and H3O moieties, between which the protons of the system were assumed to be transferred see Fig. 5.2a. 

It is certainly conceivable that some other interpretation could have been made of the difference maps, but a satisfactory feature of this model was that the final refined occupations were physically reasonable, consistent with charge neutrality requirements, and provided a plausible 

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