The H + CH 3 OH reaction, which plays an important role in combustion and the interstellar medium, presents a prototypical system with multi channels and tight transition states. However, no globally reliable potential energy surface (PES) has been available to date. Here we develop global analytical PESs for this system using the permutation-invariant polynomial neural network (PIP-NN) and the high-dimensional neural network (HD-NN) methods based on a large number of data points calculated at the level of the explicitly correlated unrestricted coupled cluster single, double, and perturbative triple level with the augmented correlation corrected valence triple-ζ basis set (UCCSD(T)-F12a/AVTZ). We demonstrate that both machine learning PESs are able to accurately describe all dynamically relevant reaction channels. At a collision energy of 20 kcal/mol, quasi-classical trajectory calculations reveal that the dominant channel is the hydrogen abstraction from the methyl site, yielding H 2 + CH 2 OH. The reaction of this major channel takes place mainly via the direct rebound mechanism. Both the vibrational and rotational states of the H 2 product are relatively cold, and large portions of the available energy are converted into the product translational motion.

Cl+CH 3 OH → HCl+CH 3 O/CH 2 OH is a prototypical multiple-channel reaction. Experimentally, ample dynamical and kinetic information is available, but there are still many uncertainties concerning the reaction mechanism. Theoretical investigations are rare due to the absence of a potential energy surface (PES), which has greatly hindered our understanding of the reaction dynamics. Using a machine-learning approach, an accurate full-dimensional PES for the title reaction based on tens of thousands of high-level ab initio data is reported. Comprehensive dynamical calculations were performed on the PES using quasi-classical trajectories, and the results provide insights into the reaction kinetics and dynamics. The calculated non-Arrhenius rate coefficients are consistent with the experimental data, attributable to a complex-forming mechanism at low temperatures. At high energies, the reaction is dominated by a direct mechanism, which results in dominant forward scattering via a stripping mechanism augmented by less prominent sideways and backward scattering via a rebound mechanism. At collision energies of 5.6 and 8.7 kcal/mol, the measured product translational energy and ro-vibrational state distributions of HCl are well reproduced. In addition, mode specificity is revealed and rationalized by the sudden vector projection model. This work sheds valuable light on the microscopic mechanism and dynamics of this prototypical multichannel reaction.

Comprehensive dynamical simulations of a prototypical multi-channel reaction on a globally accurate potential energy surface show that the non-statistical product branching is dictated by unique stereodynamics in the entrance channels.

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