High-level ab initio characterization of the multichannel Cl(²P_3/2) + C₂H₅I reaction

The potential energy surface (PES) of the Cl(²P_3/2) + C₂H₅I reaction is described by highly-accurate electronic structure computations, covering both hydrogen- and iodine-abstraction pathways and several substitution routes proceeding through either Walden inversion or front-side attack, including both atom- (H, I) and group-exchange (CH₂I, CH₃) mechanisms. Geometries and harmonic vibrational frequencies of all stationary points are determined at the MP2/aug-cc-pVDZ and CCSD(T)-F12b/aug-cc-pVDZ levels of theory, and single-point energies are further refined at the most accurate geometries using the coupled-cluster method with aug-cc-pVTZ and aug-cc-pVQZ basis sets. To target chemical accuracy, five additional energy corrections - accounting for core correlation, scalar relativistic, spin-orbit, and post-CCSD(T) effects - are incorporated into the CCSD(T)-F12b/aug-cc-pVQZ single-point energies. The resulting benchmark data allow for the detailed mapping of the reaction pathways, including the identification of transition states and pre- and post-reaction minima, which guide the system from the reactants toward the various product channels on the PES. Rate coefficients are determined using transition-state theory, including the Wigner tunneling correction, and compared to literature theoretical values.