Automated full-dimensional potential energy surface development and quasi-classical dynamics for the HI(X1σ+) + C2H5 → I(2P3/2) + C2H6 reaction

A full-dimensional spin-orbit-corrected analytical coupled-cluster-quality potential energy surface (PES) is developed for the HI(X-1 sigma(+)) + C2H5 -> I(P-2(3/2)) + C2H6 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 + C2H5 -> Br + C2H6. The reaction clearly favors H-side attack over side-on HI and the least-preferred I-side approach, and favors side-on CH3CH2 attack marginally over CH2-side and the least-preferred CH3-side approach at high E-coll. At low E-coll, however, the dominant effect of H-side attack becomes weaker, while the side-on CH3CH2 attack becomes comparable with CH2-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 C2H6 vibration. The vibrational and rotational distributions of the C2H6 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 + C2H5 -> I + C2H6 reaction is very similar to the case in the HBr + C2H5 -> Br + C2H6 system that we investigated recently.

Automated summary

In this study, a full-dimensional spin-orbit-corrected analytical coupled-cluster-quality potential energy surface (PES) is developed. Quasi-classical trajectory (QCT) simulations are performed to investigate the HI + C2H5 -> I + C2H6 reaction. The results show the collision energy dependence of reaction probability, scattering angle distribution, and attack preference at different attack sites.