Spherical electron cloud hopping molecular dynamics simulation on dissociative recombination of protonated water

Dissociative recombination (DR) of H(3)O(+) with electrons at zero collision energy has been studied by a direct ab initio molecular dynamics method on four low-lying electronic states of the system. Initial conditions for trajectories are determined by a spherical electron cloud hopping (SECH) model, while nonadiabatic effects are considered through a surface hopping scheme. The energies, forces, and nonadiabatic coupling strengths (NACS) used in trajectory propagations are calculated on-the-fly via state-average complete active self-consistent field (CASSCF) theory with full valence electrons. Dynamics results show that the H(3)O(+) DR is ultrafast and yields diversity of products. Product branching fractions are predicted to be 0.660 for (OH + 2H), 0.230 for (H(2)O + H), 0.108 for (OH + H(2)), and 0.002 for (O + H + H(2)), which are in excellent agreement with the heavy-ion storage ring experimental results. Kinetic energies of the eliminated hydrogen atoms are large and show a bimodal distribution.