Proton transfer diabatic/adiabatic

The adiabatic MOVE ground state potential surface is significantly lower in energy than the diabatic surfaces. The computed barrier for the proton transfer is 1.2 kcal/mol at the MOVE(3)/3-21G level, which may be compared with the... 

Figure 2. (a) Schematic illustration of the adiabatic (solid) and diabatic (dashed) vibrational free energy curves as functions of the solvent coordinate Zp for a symmetric single proton transfer reaction, (b) Potential energy curves as functions of the proton coordinate r, for three specific values of the solvent coordinate Zp indicated in (a). 

In principle, Eq. (1) is only valid in the diabatic regime. For proton transfer, that is considered to occur in a partially adiabatic regime, it is not strictly accurate. Nevertheless, it can still be expected to give a good upper estimate of the activation energy.)... 

In chemical dynamics, one can distinguish two qualitatively different types of processes electron transfer and reactions involving bond rearrangement the latter involve heavy-particle (proton or heavier) motion in the formal reaction coordinate. The zero-order model for the electron transfer case is pre-organization of the nuclear coordinates (often predominantly the solvent nuclear coordinates) followed by pure electronic motion corresponding to a transition between diabatic electronic states. The zero-order model for the second type of process is transition state theory (or, preferably, variational transition state theory ) in the lowest adiabatic electronic state (i.e., on the lowest-energy Bom-Oppenheimer potential energy surface). 

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