Production of vibrationally excited H2O from charge exchange of H3O+ with cesium

Vibrational excitation and product branching ratios in dissociation of the isotopologs of H3O: experiment and theory

The dissociation dynamics of the Rydberg radical H3O and the deuterated isotopologs have been studied by dissociative charge exchange of H3O(+) with Cs. Center-of-mass kinetic energy release distributions were measured with a fast-beam translational spectrometer and compared with direct dynamics quasiclassical trajectory calculations with initial conditions from an ab initio potential energy surface for H3O(+). The experimental branching fractions for dissociation of each isotopolog were obtained and compared with the calculated branching fractions. The dominant dissociation channel for all species is elimination of an H/D atom, and the water product was formed with a significant vibrational inversion in stretching vibrations that varies with the mass of the leaving atom in the dissociation. Branching fractions for the mixed isotopologs show that H atom elimination is favored over D atom elimination. Given the importance of H3O(+) in plasmas, astrochemistry, and in condensed phases, the striking energy partitioning found in this neutralization process is notable.

Hot water molecules from dissociative recombination of D3O+ with cold electrons

Individual product channels in the dissociative recombination of deuterated hydronium ions and cold electrons are studied in an ion storage ring by velocity imaging using spatial and mass-sensitive detection of the neutral reaction fragments. Initial and final molecular excitation are analyzed, finding the outgoing water molecules to carry internal excitation of more than 3 eV in 90% of the recombination events. Initial rotation is found to be substantial and in three-body breakup strongly asymmetric energy repartition among the deuterium products is enhanced for hot parent ions.

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.