New ab initio potential energy surface of NaFH (1A') system and quantum dynamics studies for the Na + HF (v, j) → NaF + H reaction.

A global potential energy surface (PES) for the electronic ground state of the Na + HF reactive system is constructed by three-dimensional cubic spline interpolation of 37 000 ab initio points obtained using the multireference configuration interaction method including the Davidson's correction (MRCI + Q) with auc-cc-pV5Z basis set. The endoergicity, well depth and properties of the separated diatomic molecules are in good agreement with experimental estimations. Quantum dynamics calculations have been performed and compared with those of the previous MRCI PES as well as experimental values. The better agreement between theory and experiment indicates the accuracy of the new PES.

Quantum Dynamics Calculations of Na (32S, 32P) + HF → NaF + H Reactions.

The dynamics of the reactive scatterings of the ground (Na(3S)) and first excited (Na(3P)) state sodium atoms from hydrogen fluoride (HF) molecules is investigated by performing comprehensive Coriolis-coupled quantum wave packet calculations on the recent ab initio potential energy surface (PES). In the Na(3S) + HF reaction, the nonadiabatic effect is found to be negligibly small, and the reactivity is significantly promoted by the initial vibrational excitations being in line with the available experimental result. Excellent quantitative agreement between theory and experiment is also achieved for the initial state specified integral cross sections and rate constants for v ≥ 3 vibrational states. However, the calculated rate constant for v = 2 significantly underestimates the experimental result. The possible cause for the disagreement is discussed in detail. For the Na(3P) + HF scattering, which can lead to the formation of either the ground state NaF + H product or Na(3S) + HF reactant via the harpooning process, the calculated result for the integral cross section shows excellent agreement with the available experimental result indicating the reasonable accuracy of the interstate coupling term of the employed PES.

A new ab initio potential energy surface of LiClH (1A') system and quantum dynamics calculation for Li + HCl (v = 0, j = 0-2) → LiCl + H reaction.

A new ab initio potential energy surface (PES) for the ground state of Li + HCl reactive system has been constructed by three-dimensional cubic spline interpolation of 36 654 ab initio points computed at the MRCI+Q/aug-cc-pV5Z level of theory. The title reaction is found to be exothermic by 5.63 kcal/mol (9 kcal/mol with zero point energy corrections), which is very close to the experimental data. The barrier height, which is 2.99 kcal/mol (0.93 kcal/mol for the vibrationally adiabatic barrier height), and the depth of van der Waals minimum located near the entrance channel are also in excellent agreement with the experimental findings. This study also identified two more van der Waals minima. The integral cross sections, rate constants, and their dependence on initial rotational states are calculated using an exact quantum wave packet method on the new PES. They are also in excellent agreement with the experimental measurements.

Quantum and classical dynamics of H + CaCl(X (2)Σ(+)) → HCl + Ca((1)S) reaction and vibrational energy levels of the HCaCl complex.

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.