THE ROLE OF COUPLING IN INTRAMOLECULAR PROTON-TRANSFER REACTIONS - THE HYDROGEN OXALATE ANION AS AN EXAMPLE

Coupling between the proton motion and the internal degrees of freedom for intramolecular proton transfer in the hydrogen oxalate anion has been studied. A normal mode analysis at a sequence of points along the Intrinsic Reaction Coordinate (IRC) has been performed and the coupling functions B(k,F) have been obtained. It is shown that, although for the reactant the IRC direction essentially consists of the motion of oxygen atoms, the coupling changes this IRC direction towards the motion corresponding to proton transfer itself. From a quantum point of view, the curvature that appears as a consequence allows comer-cutting tunneling. Finally, the effect of isotope substitution is considered.