Potential traps for an excess electron in liquid water: the trap lifetime distributions

The possibilities of trapping of an excess electron by potential fluctuations in liquid water have been investigated by means of the computer simulation method. The configurations of water molecules generated by the Molecular Dynamics simulation were searched for local minima of the potential energy. The analysis of a large set of the minima allows us to obtain a statistical description of the microscopic trapping sites, including the distributions of the trap energy, trapping power and volume. The estimated concentration of the electron traps in liquid water is about 0.5 M. The possibility of electron trapping depends very strongly on the lifetime of the potential traps. The simulations yielded the distribution of the trap lifetime with the average of 84 fs. A substantial fraction (20%) of the traps live longer than 100 fs: a small fraction (0.2%) live as long as I ps. The experimental measurements of the electron hydration time give the results of the order of 100 fs. Thus, the values of the trap lifetime obtained from our simulations support the 'trap seeking' mechanism of the electron localization in water.