A SIMPLE-MODEL FOR PROTON-TRANSFER

A simple model is presented for the study of proton transfer in hydrog en bonds. The energetics and dynamics of a simplified unidimensional p roton coordinate under the presence of an effective potential is consi dered. The transfer of a proton from one nucleus to another depends on the effective potential at each site and the coupling between the two electronic states. The model describes these features with three fact ors: the geometry of the system, the non-bonding interaction, and the electronic coupling strength. The validity of a two level approximatio n for proton transfer is considered. The transition from a two level t o a non-two level system is dependent on the effective hydrogen bond l ength R used, the electronic coupling T-AB, and the non-bonding intera ction strength represented by Delta nu. For a reasonable range of T-AB (0.5-2.5 eV) and Delta nu (350-550 cm(-1)) the transition occurs for R = 2.6-2.9 Angstrom. The application of the model to realistic system s is discussed.