Proton-lattice coupled model

The modelling just described of the direct HC1 + CIONO2 reaction on an ice lattice to produce molecular chlorine and ionized nitric acid portrayed a relatively facile coupled proton transfer/SN2 mechanism, evidently supported in subsequent calculations.26 These results also reinforced the idea of an ionic pathway involving ionized HC1,912>21 as opposed to molecular HC1. 

The simplest analytic model for an isolated proton in a lattice assumes that it is situated in a potential well centred on an interstitial site. This model is particularly appropriate to protons in a transition metal lattice, where the electron from the hydrogen atom can be accommodated in the d-band of the metal, but is also applicable to many other cases as well - e.g. to molecular hydrogen trapped in ion-exchanged zeolites (see Section 6.8.2 below). The model assumes that there are no interactions between neighbouring hydrogen atoms and that there is little coupling with the lattice modes. This implies that M/wjp 1 where m is the mass of the proton and M is the mass of the lattice atom. In transition metals, with face-centred cubic (FCC), body-centred cubic (BCC) or hexagonal close packed (HCP) lattices, the proton normally sits on either octahedral or tetrahedral sites. In more complex intermetallic... 

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