A simple model for proton transfer Original Research Article

A simple model is presented for the study of proton transfer in hydrogen bonds. The energetics and dynamics of a simplified unidimensional proton coordinate under the presence of an effective potential is considered. 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 factors: the geometry of the system, the non-bonding interaction, and the electronic coupling strength. The validity of a two level approximation for proton transfer is considered. The transition from a two level to a non-two level system is dependent on the effective hydrogen bond length R used, the electronic coupling TAB, and the non-bonding interaction strength represented by Δv. For a reasonable range of TAB (0.5–2.5 eV) and Δv (350–550 cm−1) the transition occurs for R = 2.6–2.9 Å. The application of the model to realistic systems is discussed.