Automated full-dimensional potential energy surface development and quasi-classical dynamics for the HI(X 1 Σ + ) + C 2 H 5 → I( 2 P 3/2 ) + C 2 H 6 reaction.

A full-dimensional spin-orbit-corrected analytical coupled-cluster-quality potential energy surface (PES) is developed for the HI(X 1 Σ + ) + C 2 H 5 → I( 2 P 3/2 ) + C 2 H 6 reaction using the ROBOSURFER program package, and a quasi-classical trajectory (QCT) study on the new PES is reported. The stationary-point relative energies obtained on the PES reproduce well the benchmark values. Our simulations show that in the 0.5-40 kcal mol -1 collision energy ( E coll ) range, the b = 0 reaction probability, where b denotes the impact parameter, increases first and then stays steady with increasing E coll , reaching around 10% when E coll = 5 kcal mol -1 . No significant E coll dependence is observed in the range of 5-40 kcal mol -1 . The reaction probabilities decrease monotonically with increasing b , and the maximum b where the reactivity vanishes becomes smaller and smaller as E coll increases. Scattering angle distributions show a forward scattering preference, indicating the dominance of the direct stripping mechanism, which is more obvious than in the case of HBr + C 2 H 5 → Br + C 2 H 6 . The reaction clearly favors H-side attack over side-on HI and the least-preferred I-side approach, and favors side-on CH 3 CH 2 attack marginally over CH 2 -side and the least-preferred CH 3 -side approach at high E coll . At low E coll , however, the dominant effect of H-side attack becomes weaker, while the side-on CH 3 CH 2 attack becomes comparable with CH 2 -side and the former is a little less favored when E coll = 0.5 kcal mol -1 . It turns out that the initial translational energy is converted 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 none of the reactive trajectories violates the zero-point energy (ZPE) constraint. The energy transfer in the HI + C 2 H 5 → I + C 2 H 6 reaction is very similar to the case in the HBr + C 2 H 5 → Br + C 2 H 6 system that we investigated recently.