Experimental Resonance-Like Features in the Barrierless Reaction of O(¹D) + D₂ at Collision Energies from 20 to 168 cm–1

Reaction resonances have been extensively studied in barrier reactions, whereas the observation of reaction resonances is rarely reported in barrierless reactions. In this work, a high-resolution crossed molecular beam experiment using the D atom Rydberg tagging technique was systematically carried out to investigate the barrierless reaction of O(1D) + D2 → OD + D over a collision energy range of 20-168 cm-1. Four experimental observations were found, including the dramatic changes of OD product angular distributions, the peak structures of collision energy-dependent differential cross sections (DCSs) in the forward and backward scattering directions, the ridge features in the 3D-DCS plot of σ(θ, Ec), and the valley structure of the collision energy-dependent integral cross section. These resonance-like features may offer fresh insights into the intricate dynamics of this prototype barrierless reaction at low collision energies.