MODELING PROTON-TRANSFER POTENTIALS IN ANGULARLY DEFORMED HYDROGEN-BONDS

Earlier work demonstrated that either a simple fourth-order polynomial or a pair of Morse functions could be fit with high accuracy to model proton transfers across H-bonds. The work is extended here to a systematic set of angular distortions in the H2O..H+..OH2 and H3N.. H+.. NH3 systems. So long as the deformation does not impose a left-right asymmetry into the system, either of these types of functions can reproduce ab initio transfer potentials well. But the Morse potentials are superior in that neither stretches nor bends of the H-bonds cause large variation in the parameters. For those modes of angular distortion which introduce asymmetry into the transfer potential, the ab initio data can be accommodated by permitting small variations in two of the parameters in the Morse functions. (C) 1993 John Wiley & Sons, Inc.