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Time-dependent quantum mechanical calculations have been carried out to estimate the total reactive cross sections, product branching ratios, and product quantum state distributions for the O(¹D) + HCl reaction using both reactant and product Jacobi coordinates. The potential energy surface of T. Martinez et al. (Phys. Chem. Chem. Phys. 2000, 2, 589) has been used in the calculations. The theoretical predictions are compared with experimental results and with the results of classical trajectory calculations on the same surface. The comparisons demonstrate the suitability of the potential energy surface and provide useful insights into the reaction mechanism. The calculations using product Jacobi coordinates are the first calculations for this system which permit the prediction of state-to-state reaction probabilities and of product quantum state distributions.

A theoretical study of the highest bound states and some of the lowest energy resonance states of water in its ground electronic state, &Xtilde; = 1¹A‘, and with zero total angular momentum, is presented. The majority of our calculations correspond to the even symmetry block with respect to hydrogen atom exchange. An accurate ab initio based potential surface is employed. The Lanczos method, applied to a large grid representation of the Hamiltonian, is shown to be a straightforward method for obtaining the bound state energy levels. Selected eigenfunctions are also determined and several of those near the dissociation threshold are quite extended. Resonance states just above the dissociation threshold are characterized with the aid of damped Chebyshev iterations. Among the resonances observed are those with hyperspherical and local mode character.

The real wave packet method is used to calculate state-to-state reaction probabilities and branching ratios for the reaction O(¹D) + HD → OH(OD) + D(H) for zero total angular momentum. Calculations are performed on the adiabatic potential energy surfaces corresponding to the &Xtilde;¹A‘ and 1¹A‘ ‘ electronic states. Vibrational state-to-state cross sections, product state distributions and branching ratios are estimated using a capture model and J-shifting methods. The results are compared with experiment and with results of quasi-classical trajectory calculations.

We develop a wave packet approach to treating the electronically nonadiabatic reaction dynamics of O(¹D) + H2 → OH + H, allowing for the 1¹A‘ and 2¹A‘ potential energy surfaces and couplings, as well as the three internal nuclear coordinates. Two different systems of coupled potential energy surfaces are considered, a semiempirical diatomics-in-molecules (DIM) system due to Kuntz, Niefer, and Sloan, and a recently developed ab initio system due to Dobbyn and Knowles (DK). Nonadiabatic quantum results, with total angular momentum J = 0, are obtained and discussed. Several single surface calculations are carried out for comparison with the nonadiabatic results. Comparisons with trajectory surface hopping (TSH) calculations, and with approximate quantum calculations, are also included. The electrostatic coupling produces strong interactions between the 1¹A‘ and 2¹A‘ states at short range (where these states have a conical intersection) and weak but, interestingly, nonnegligible interactions between these states at longer range. Our wave packet results show that if the initial state is chosen to be effectively the 1A‘ state (for which insertion to form products occurs on the adiabatic surface), then there is very little difference between the adiabatic and coupled surface results. In either case the reaction probability is a relatively flat function of energy, except for resonant oscillations. However, the 2A‘ reaction, dynamics (which involves a collinear transition state) is strongly perturbed by nonadiabatic effects in two distinct ways. At energies above the transition state barrier, the diabatic limit is dominant, and the 2A‘ reaction probability is similar to that for 1A‘ ‘, which has no coupling with the other surfaces. At energies below the barrier, we find a significant component of the reaction probability from long range electronic coupling that effectively allows the wave packet to avoid having to tunnel through the barrier. This effect, which is observed on both the DIM and DK surfaces, is estimated to cause a 10% contribution to the room temperature rate constant from nonadiabatic effects. Similar results are obtained from the TSH and approximate quantum calculations.