We report two novel roaming pathways for the H + C 2 H 2 → H 2 + C 2 H reaction by performing extensive quasiclassical trajectory calculations on a new, global, high-level machine learning-based potential energy surface. One corresponds to the acetylene-facilitated roaming pathway, where the H atom turns back from the acetylene + H channel and abstracts another H atom from acetylene. The other is the vinylidenefacilitated roaming, where the H atom turns back from the vinylidene + H channel and abstracts another H from vinylidene. The "double-roaming" pathways account for roughly 95% of the total cross section of the H 2 + C 2 H products at the collision energy of 70 kcal/ mol. These computational results give valuable insights into the significance of the two isomers (acetylene and vinylidene) in chemical reaction dynamics and also the experimental search for roaming dynamics in this bimolecular reaction.
So far, numerous researches on the He 2 H À system have still been restricted to several analytical forms of the potential energy interaction, where the calculations in the three-body interaction may be not precise. With that in mind, we have provided an accurate, global, full-dimensional potential energy surface (PES) for the ground state of the He 2 H À system by the fundamental invariant neural network (FI-NN) fitting based on roughly 45 000 ab initio data points. The energy points are calculated with the coupled-cluster singles and doubles with perturbative triples (CCSD [T]) method using the augmented Dunning-type correlation-consistent (aug-cc-pVTZ, aug-cc-pVQZ and aug-cc-pV5Z) basis sets, respectively. Based on adoption and comparison of three different extrapolation formulas, we obtained even accurate data points, which are extrapolated to the complete basis set (CBS) limit. The overall root mean square error of the fitting PES is only about 6.314 Â 10 À3 cm À1 . It can be expected that this accurate PES would provide insights to further interesting discoveries in dynamics or spectroscopies for the relevant molecular systems.
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