One-dimensional and bidimensional tunneling splittings have been calculated in malonaldehyde (MA) and hydrogenoxalate anion (HX) systems. Two different monodimensional paths have been considered: the intrinsic reaction path (IRP) and the linear reaction path (LRP). A bidimensional model that includes the coupling between the proton transfer motion and the vibration of the heavy atoms is then used. We find that with the bidimensional model the splittings are 2 orders of magnitude greater than the monodimensional ones, and close to the previous experimental and theoretical values for the MA when zero point energy is introduced. At all levels of calculation we obtain that the splitting is greater in the MA than in the HX. This fact is attributed to the different size of the rings through which the proton transfer occurs.

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ENRIC BOSCH, MIQUEL MORENO, and JOSE M A R~A LLUCH. Can. J. Chem. 70, 100 (1992).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,,, 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.Key words: intramolecular proton transfer, coupling functions, IRC curvature, tunneling splitting, isotope substitution.ENRIC BOSCH, MIQUEL MORENO et JOSE M A R~A LLUCH. Can. J. Chem. 70, 100 (1992).On a CtudiC le couplage entre le mouvement du proton et les degres de IibertC interne du transfert protonique intramolCculaire dans l'anion hydrogenoxalate. On a fait un analyse des modes propres de vibration sur une sequence de points de la coordonnCe rCactionnelle (CRI) et on a pu en tirt les fonctions de couplage B,,, . On a dCmontrC que, bien que la direction de la CRI dans le rCactif peut &tre dCcrite principalement par le mouvement des atomes d'oxygkne, le couplage change cette direction de la CRI vers le mouvement correspondant au transfert protonique lui-mCme. D'un point de vue quantique, la courbure qui apparait rend possible un effet tunnel qui coupe les coins. Enfin, on a considere I'effet de la substitution isotopique.Mots clPs : transfert protonique intramoleculaire, fonctions de couplage, courbure de la CRI, dedoublement provoquC par I'effet tunnel, substitution isotopique.[Traduit par la rCdaction]