Proton transfer in the [M••• H•••NH3]+ system (M=1,4-dioxane)

By fixing the hydrogen bond length (0(...)H(...)N) at a value, the potential energy curves of the [(MHNH3)-H-...-N-...](+) were explored at the HF/6-31G(d) and B3LYP/6-31G(d) level of theory. The calculations indicate that as the hydrogen bond length is increased, the proton transfer barrier increases and the single-well potential energy curve tends to become double-welled. To model the proton transfer (PT) in 'real' system, the transition state connecting M-...(H-NH3)(+) and (M-H)+...NH3 has been optimized and the reaction path gives an estimate of the PT barrier. Correlated electronic structure calculation, coupled with ZPE correction, provides a better understanding of the PT barrier. (C) 2002 Elsevier Science B.V. All rights reserved.