The effect of reagent translation on the reaction dynamics and the absolute reaction cross section of H+H2O→OH+H2

State-to-state quantum reactive scattering for four-atom chemical reactions: Differential cross section for the H+H2O→H2+OH abstraction reaction

The time-dependent wave packet method was extended to calculate the state-to-state differential cross section for the title four-atom abstraction reaction with H2O in the ground rovibrational state. One spectator OH bond length was fixed in the study, but the remaining five degrees of freedom were treated exactly. It was found that (a) the differential cross section changes from being strongly backward peaked at low collision energy to sideward scattering at E = 1.4 eV, and (b) the rotational state-resolved differential cross section for H2 differs substantially from that for OH.

Product spin–orbit state resolved dynamics of the H+H2O and H+D2O abstraction reactions

The product state-resolved dynamics of the reactions H+H(2)O/D(2)O-->OH/OD((2)Pi(Omega);v',N',f )+H(2)/HD have been explored at center-of-mass collision energies around 1.2, 1.4, and 2.5 eV. The experiments employ pulsed laser photolysis coupled with polarized Doppler-resolved laser induced fluorescence detection of the OH/OD radical products. The populations in the OH spin-orbit states at a collision energy of 1.2 eV have been determined for the H+H(2)O reaction, and for low rotational levels they are shown to deviate from the statistical limit. For the H+D(2)O reaction at the highest collision energy studied the OD((2)Pi(3/2),v'=0,N'=1,A') angular distributions show scattering over a wide range of angles with a preference towards the forward direction. The kinetic energy release distributions obtained at 2.5 eV also indicate that the HD coproducts are born with significantly more internal excitation than at 1.4 eV. The OD((2)Pi(3/2),v'=0,N'=1,A') angular and kinetic energy release distributions are almost identical to those of their spin-orbit excited OD((2)Pi(1/2),v'=0,N'=1,A') counterpart. The data are compared with previous experimental measurements at similar collision energies, and with the results of previously published quasiclassical trajectory and quantum mechanical calculations employing the most recently developed potential energy surface. Product OH/OD spin-orbit effects in the reaction are discussed with reference to simple models.

Cross section for the H+H2O abstraction reaction: experiment and theory

The absolute value of the cross section for the abstraction reaction between fast H atoms and H2O has been determined experimentally at a mean collision energy of 2.46 eV. The OH population distribution at the same mean energy has also been determined. The new measurements are compared with state-of-the-art quantum mechanical and quasiclassical scattering calculations on the most recently developed potential energy surface.

The dynamics of the H + H2O reaction

This article reviews the history and recent progress in the study of the dynamics of the H + H2O reaction, which has become a benchmark for experimental research in the field of gas-phase reaction dynamics. The dynamics of H + H2O is discussed in terms of the different observable properties: integral cross-sections, rate coefficients, product state distributions, differential cross-sections, and vector correlations. It is shown how experimental measurements and first-principle theoretical calculations have revealed the interesting microscopic aspects of this elementary chemical reaction.

State-to-state chemical reaction dynamics in polyatomic systems: case studies

This review illustrates the experimental study of chemical reaction dynamics using methods that select the quantum states and energy of the reactants and determine the quantum states and energy of the products. The focus is reaction dynamics in systems in which at least one of the reactants or products is a polyatomic molecule. The approach taken is to select four prototype reaction systems as case studies to demonstrate the detail of information and insight that can come from such experiments. Thus, the review is selective and neither claims nor attempts to be comprehensive. Reference to and discussion of theoretical reaction dynamics are included where computational results directly connect with the experiments.

First-principles theory for the H + H2O, D2O reactions

A full quantum dynamical study of the reactions of a hydrogen atom with water, on an accurate ab initio potential energy surface, is reported. The theoretical results are compared with available experimental data for the exchange and abstraction reactions in H + D2O and H + H2O. Clear agreement between theory and experiment is revealed for available thermal rate coefficients and the effects of vibrational excitation of the reactants. The excellent agreement between experiment and theory on integral cross sections for the exchange reaction is unprecedented beyond atom-diatom reactions. However, the experimental cross sections for abstraction are larger than the theoretical values by more than a factor of 10. Further experiments are required to resolve this.

Quantum theory of chemical reaction dynamics

It is now possible to use rigorous quantum scattering theory to perform accurate calculations on the detailed state-to-state dynamics of chemical reactions in the gas phase. Calculations on simple reactions, such as H + D2 --> HD + D and F + H2 --> HF + H, compete with experiment in their accuracy. Recent advances in theory promise to extend such accurate predictions to more complicated reactions, such as OH + H2 --> H2O + H, and even to reactions of molecules on solid surfaces. New experimental techniques for probing reaction transition states, such as negative-ion photodetachment spectroscopy and pump-probe femtosecond spectroscopy, are stimulating the development of new theories.

OH-H2ENTRANCE CHANNEL COMPLEXES

The entrance channel to the OH+H2-->H2O+H hydrogen abstraction reaction has been investigated from several different experimental approaches and complementary theoretical calculations. Weakly bound complexes between the hydroxyl radical and molecular hydrogen have been stabilized within a shallow well in the entrance channel and characterized via electronic spectroscopy on the OH A2Sigma+-X2Pi transition. Laser-induced fluorescence and fluorescence depletion experiments have revealed the binding energy of H2/D2 with ground state OH X2Pi radicals, the intermolecular energy levels supported by the OH A2Sigma+ (v'=0,1)+H2/D2 potential, and the OH-H2/D2 excited state dissociation limit. The OH X2Pi + H2 potentials have also been examined through inelastic scattering measurements on Lambda-doublet state-selected OH with normal or para-H2. Finally, photodetachment of an electron from the H3O- anion enabled the neutral reaction to be probed in conformations sampled by the two isomeric forms of the anion.