Quasiclassical Trajectory Study of Energy and Angular Distributions for the H + CO₂ → OH + CO Reaction^†

An extensive study of the H + CO₂ → OH + CO reaction dynamics has been carried out by means of the quasiclassical trajectory method employing three potential energy surfaces (PESs). The first PES corresponds to the earlier Bradley and Schatz (BS) surface. In the second PES (BSH), the BS surface was modified to include a new term that describes the OH + CO exit channel barrier and van der Waals region, based on high-level ab initio calculations. The third surface (LTSH) corresponds to a modification of the BSH surface where the energies of the various stationary points outside the exit channel region are calibrated from new ab initio calculations. We find that the correction in the exit channel improves the description of the energy partitioning to products, with both BSH and LTSH giving less release to translation and more to CO rotation than BS. These new results are in better agreement with measured product energy partitioning results, and we also find that the LSTH surface gives angular distributions that are in excellent agreement with experiment. Rovibrational state-resolved energy and angular distributions are also discussed. Details of the microscopic reaction mechanism are evaluated on the basis of an analysis of the dynamics as a function of the HOCO complex lifetime, leading to trends that provide insight on the complex-forming reaction fundamentals. In particular we find that the product internal distributions are independent of complex lifetime, while the angular distributions are strongly correlated with lifetime. The often used osculating complex model describes the angular distributions accurately for lifetimes shorter than half the rotational period but becomes inaccurate at longer times.