Full-dimensional potential energy surface development and dynamics for the HBr + C 2 H 5 → Br( 2 P 3/2 ) + C 2 H 6 reaction.

We report a full-dimensional spin-orbit-corrected analytical potential energy surface (PES) for the HBr + C 2 H 5 → Br + C 2 H 6 reaction and a quasi-classical dynamics study on the new PES. For the PES development, the ROBOSURFER program package is applied and the ManyHF-based UCCSD(T)-F12a/cc-pVDZ-F12(-PP) energy points are fitted using the permutationally-invariant monomial symmetrization approach. The spin-orbit coupling at the level of MRCI-F12+Q(5,3)/cc-pVDZ-F12(-PP) is taken into account, since it has a significant effect in the exit channel of this reaction. Our simulations show that in the 1-40 kcal mol -1 collision energy ( E coll ) range the b = 0 reaction probability increases first and then decreases with increasing E coll , reaching around 15% at the medium E coll . No significant E coll dependence is observed in the range of 5-20 kcal mol -1 . The reaction probabilities decrease monotonically with increasing b and the maximum b where reactivity vanishes is smaller and smaller as E coll increases. Unlike in the case of HBr + CH 3 , the integral cross-section decays sharply as E coll changes from 5 to 1 kcal mol -1 . Scattering angle distributions usually show forward scattering preference, indicating the dominance of the direct stripping mechanism. The reaction clearly favors H-side attack over side-on HBr and the least-preferred Br-side approach, and favors side-on CH 3 CH 2 attack over the CH 2 -side and the least-preferred CH 3 -side approach. The initial translational energy turns out to convert mostly into product recoil, whereas the reaction energy excites the C 2 H 6 vibration. The vibrational and rotational distributions of the C 2 H 6 product slightly blue-shift as E coll increases, and very few reactive trajectories violate zero-point energy.