Dynamics of the HCl + C₂H₅ Multichannel Reaction on a Full-Dimensional Ab Initio Potential Energy Surface

We report a full-dimensional ab initio analytical potential energy surface (PES), which accurately describes the HCl + C₂H₅ multichannel reaction. The new PES is developed by iteratively adding selected configurations along HCl + C₂H₅ quasi-classical trajectories (QCTs), thereby improving our previous Cl(²P_3/2) + C₂H₆ PES using the Robosurfer program package. QCT simulations for the H'Cl + C₂H₅ reaction reveal hydrogen-abstraction, chlorine-abstraction, and hydrogen-exchange channels leading to Cl + C₂H₅H', H' + C₂H₅Cl, and HCl + C₂H₄H', respectively. Hydrogen abstraction dominates in the collision energy (E_coll) range of 1-80 kcal/mol and proceeds with indirect isotropic scattering at low E_coll and forward-scattered direct stripping at high E_coll. Chlorine abstraction opens around 40 kcal/mol collision energy and becomes competitive with hydrogen abstraction at E_coll = 80 kcal/mol. A restricted opening of the cone of acceptance in the Cl-abstraction reaction is found to result in the preference for a backward-scattering direct-rebound mechanism at all energies studied. Initial attack-angle distributions show mainly side-on collision preference of C₂H₅ for both abstraction reactions, and in the case of the HCl reactant, H/Cl-side preference for the H/Cl abstraction. For hydrogen abstraction, the collision energy transfer into the product translational and internal energy is almost equally significant, whereas in the case of chlorine abstraction, most of the available energy goes into the internal degrees of freedom. Hydrogen exchange is a minor channel with nearly constant reactivity in the E_coll range of 10-80 kcal/mol.