Nonadiabatic molecular dynamics simulation of photoexcitation experiments for the solvated electron in methanol

Nonadiabatic quantum molecular dynamics simulations have been performed to simulate the pump-and-probe photoexcitation experiments of the ground state equilibrium solvated electron in methanol carried out by Barbara et al. [C hem. Phys. Lett. 232, 135 (1995)]. We have characterized both the time evol ution of the quantum solute, the solvated electron, and the solvation respo nse of the classical methanol bath. The quantum energy gap provides an exce llent tool to gain insight into the underlying microscopic details of the s olvation process. The solvent response is characterized for both processes by a fast Gaussian component and a biexponential decay. The present results suggest that the residence time of the solvated electron in the first exci ted state is substantially longer than inferred from the cited experiments. The experimentally observed fast exponential portion of the relaxation mor e likely corresponds to the adiabatic solvent response than to the lifetime of the excited state electron. By comparing to photoexcitation simulations in water, it is shown that the simulated excited state lifetime is about t hree times longer in methanol than in water, predicting a less substantial increase than a recent calculation based on nonadiabatic coupling elements alone. Hydrogen-bonding statistical analysis provides interesting additiona l details about the dynamics. We find that the hydrogen-bonding network is significantly different in the first solvent shell around the electron in g round and first excited states, the distribution around the latter, larger and more diffuse, ion resembling more that of the pure liquid. Transformati on of the corresponding hydrogen bonding structures takes place on a 1 ps t ime scale. (C) 1999 American Institute of Physics. [S0021-9606(99)51922-3].