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Adiabatic (1A′ or 1A′′ state) and non-adiabatic (2A′/1A′ states) quantum dynamics calculations have been carried out for the title reaction (O(1D) + D2 → OD + D) to obtain the initial state-specified (vi = 0, ji = 0) integral cross section and rate constant using the potential energy surfaces of Dobbyn and Knowles. A total of 50 partial wave contributions have been calculated using the Chebyshev wave packet method with full Coriolis coupling to achieve convergence up to the collision energy of 0.28 eV. The total integral cross section and rate constant are in excellent agreement with experimental as well as quasi-classical trajectory results. Contributions from the adiabatic pathway of the 1A′′ state and the non-adiabatic pathway of the 2A′/1A′ states, increase significantly with the collision energy. Compared to the O(1D) + H2 system, the kinetic isotope effect (k(D)/k(H)) is found to be nearly temperature independent above 100 K and its value of 0.77 ± 0.01 shows excellent agreement with the experimental result of 0.81. [ABSTRACT FROM AUTHOR]

State-to-state differential and integral cross sections for the title reaction have been calculated using a dynamically exact quantum mechanical wave packet method on the ab initio ground H2O(X 1A′) electronic state potential energy surface of Dobbyn and Knowles. We focus on the energy dependence of the cross sections up to 0.15 eV. The total integral cross section and rate constant, obtained by summing the state-to-state integral cross sections over all open product rovibrational channels, are in excellent agreement with experimental measurements. Also in agreement with experimental data, the OH product is found to have highly inverted rotational state distributions and monotonically decaying vibrational state distributions. The calculated total differential cross section is roughly forward-backward symmetric, consistent with experimental data. The vibrational state-resolved differential cross sections are found to depend on the collision energy. The calculated results confirm the dominance of the insertion mechanism and provide a stringent test of the potential energy surface. [ABSTRACT FROM AUTHOR]

A new global potential-energy surface for the ground electronic state of NH2(X 2A″) has been constructed by three-dimensional cubic spline interpolation of more than 20 000 ab initio points, which were calculated at the multireference configuration-interaction level with Davidson correction using the augmented correlation-consistent polarized valence quadruple-zeta basis set. The new potential is shown to yield better overall agreement with the experimental vibrational frequencies of NH2 and its isotopomers. In addition, the rate constant for the N(2D)+H2(X 1Σg+)→NH(X 3Σ-)+H(2S) reaction was calculated up to 600 K and the agreement with experimental data is substantially improved over previous results. [ABSTRACT FROM AUTHOR]

Low-lying resonances of the CH2(ã 1A1) system (J=0) in an accurate ab initio potential energy surface are studied using a filter-diagonalization method. The width of these resonances fluctuates by more than two orders of magnitude and on average increases with the energy. Analysis of the resonance states concludes that the unimolecular decay of the excited molecular system near the dissociation threshold is neither mode specific nor statistical state specific. This is apparently due to remnant regularity embedded in the largely chaotic classical phase space, as evidenced by periodic orbit analysis. As a result, the Rice–Ramsperger–Kassel–Marcus and statistical adiabatic channel models overestimate the average unimolecular decay rate. The implications of the resonances for the bimolecular C(1D)+H2 reaction are also discussed. [ABSTRACT FROM AUTHOR]

We carried out accurate quantum wave packet as well as quasi-classical trajectory (QCT) calculations for H + CaCl (νi = 0, ji = 0) reaction occurring on an adiabatic ground state using the recent ab initio potential energy surface to obtain the quantum and QCT reaction probabilities for several partial waves (J = 0, 10, and 20) as well as state resolved QCT integral and differential cross sections. The complete list of vibrational energy levels supported by the intermediate HCaCl complex is also obtained using the Lanczos algorithm. The QCT reaction probabilities show excellent agreement with the quantum ones except for the failure in reproducing the highly oscillatory resonance structure. Despite the fact that the reaction is exothermic and the existence of a barrier that is energetically lower than the bottom of the reactant valley, the reaction probability for J = 0 shows threshold-like behavior and the reactivity all through the energies is very low (＜0.1). The dynamical features at two different energy regions (＜0.35 eV and ＞0.35 eV) are found to be different drastically from each other. The analyses of these results suggest that the reaction is governed by one of the two different types of reaction mechanism, one is the direct mechanism at the high energy region and the other is the indirect mechanism at the low energy region by which the reaction proceeds through the long-lived intermediate complex followed by a statistical dissociation into asymptotic channels. [ABSTRACT FROM AUTHOR]