HYDRATION SHELL EXCHANGE KINETICS - AN MD STUDY FOR NA+(AQ)

A molecular dynamics simulation method for the first hydration shell e xchange kinetics is described and is illustrated for Na+ in water. The exchange process is found to have a complex character. A calculated s mall transmission coefficient, K approximate to 0.21, indicates that t ransition-state theory seriously overestimates the rate. Grote-Hynes t heory is unsuccessful in accounting for the kappa value. This is trace d to trajectory mechanistic aspects for which the theory's assumptions break down. Inclusion of anharmonicity via the theory of Voth provide s an improved estimate.