The role played by solvent molecular flexibility in the dynamics of the solvation of an initially energetically excited excess electron in water is investigated using nonadiabatic molecular dynamics simulation and a classical flexible water model. It is found that the effect of flexibility on relaxation times is substantial, but the effect on the branching ratio for excess electrons passing through alternative intermediate excited states is small. Examination of the optical absorption spectra of the hydrated electron shows that the effect of solvent flexibility is also small here. An analysis of transient spectra supports the validity of a kinetic analysis based on species with individual well defined signatures. However, the data suggest that a two state analysis of the dynamics neglects a potentially important role for early time delocalized electrons.

Previous analysis of the computer simulation of the relaxation of energetic excess electrons in liquid water (Keszei E.; et al. J. Chem. Phys. 1993, 99, 2004) has led to a detailed molecular level and kinetic picture of this process, including the presence of multiple pathways to the equilibrium ground state. In order to explore the validity of this view, simulation results are directly compared to two available data sets obtained experimentally via ultrafast absorption spectroscopy. The analysis is carried out, first, by convolution of the simulated instantaneous spectral response of the electron with an appropriate instrumental response function. The difference between the resulting data and the reported experimental observations is no larger than the difference between the two experimental data sets. It is further shown by separate analysis that the mechanism of relaxation apparent in the simulation is kinetically consistent with the available experimental data. It is pointed out that a number of available, and apparently different, hypotheses for the sequence of species present during electronic relaxation share key features with this mechanism. Taken together, these considerations support the validity of the microscopic processes evident in simulation and emphasize the limitations inherent in the analysis of the experimentally determined spectral dynamics.

Instantaneous normal mode analysis of hydrated electron solvation dynamicsAqueous solvation dynamics with a quantum mechanical Solute: Computer simulation studies of the photoexcited hydrated electron

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Articles you may be interested inCommunication: On the consistency of approximate quantum dynamics simulation methods for vibrational spectra in the condensed phase Multidimensional quantum eigenstates from the semiclassical dynamical basis set A semiclassical approximation to quantum dynamics We present a new semiclassical formalism for nonadiabatic dynamics of a quantum subsystem interacting with an explicit bath. The method is based on a stationary phase approach to the bath and a variational principle for the quantum transition amplitudes, for quantum systems represented by approximate wave functions. A new expression for the force exerted on a classical bath by a quantum subsystem is derived which, in the adiabatic limit, reduces to the gradient of the expectation value of the energy. Our new methods for adiabatic and nonadiabatic dynamics are applied to a test problem of vibrational relaxation. For adiabatic dynamics, we find that our new algorithm produces results which converge faster, with increasing basis set size, than calculations performed with the Hellmann-Feynman force; for a limited basis set, our new algorithm gives results that are in better agreement with exact results. For nonadiabatic dynamics, we also find that, in comparison to an earlier algorithm, our new algorithm produces results which converge more rapidly with increasing basis set size. In addition, we find that our new algorithm is more robust with respect to the size of the time step than the earlier algorithm, a result of the implementation of a nuclear coordinate dependent basis.