Quantum state-to-state reaction dynamics of F + HD → HF + D via a single partial wave shape resonance state.

Understanding how reactions proceed through the transition state is central to chemistry, but isolating quantum resonance effects is challenging, especially above the reaction barrier where direct pathways usually dominate. Here we show that a single partial wave shape resonance, temporary trapping of the reacting partners behind an angular‑momentum barrier, can control the reaction F(2P3/2) + HD(v = 0, j = 0) → HF + D at a collision energy of 2.90 kcal mol-1. High-resolution crossed molecular beams scattering imaging reveals persistent oscillations across the full scattering‑angle range for the HF(v'=3, j'=1) product channel. Quantum dynamics calculations trace these oscillations to a quasibound D-HF(v'=3, L = 21) complex in the post-transition‑state region with a lifetime of about 50 fs. These results provide a clear, fully state‑resolved example of resonance‑governed reactive scattering above the barrier, linking selected reactant and product quantum states through an identifiable intermediate resonance state.