Quantum Wave Packet Study of the O(3P) + DBr → OD + Br Reaction: Cross Sections, Rate Constants, and Initial State...

We present accurate Chebyshev wave packet calculations for the title reaction using a recent ab initio potential energy surface. Integral cross sections (ICSs) and rate constants (RCs) are obtained, and the effects of initial rotational excitation (ji = 0-10, 15, 22) on the dynamics are systematically investigated. The ICSs exhibit smooth, monotonically increasing behavior with collision energy, apart from low-energy resonance structures likely arising from two van der Waals wells. Initial rotational excitation is found to enhance reactivity for ji ≥ 4, while inhibiting it for ji ≤ 3. The calculated thermal RCs show reasonable agreement with available experimental measurements, with the theoretical values slightly overestimating the experimental ones. The agreement on temperature dependence and isotopic effect is particularly encouraging. The temperature dependences of both the calculated and experimental RCs follow Arrhenius behavior by and large, with curvatures being observed in the Arrhenius plots. The fact that the curvature, which occurs at low temperatures, is more pronounced for the O(3P) + HBr system than for the heavier O(3P) + DBr system suggests the influence of tunneling. Isotopic substitution of H by D significantly reduces both ICSs at low energies and RCs across the entire temperature range (100-800 K), with differences of up to 2 orders of magnitude at low temperatures due to the large disparity in tunneling ability between the two systems.