Observation of Feshbach Resonances in the F + H 2 → HF + H Reaction

Reaction resonances, or transiently stabilized transition-state structures, have proven highly challenging to capture experimentally. Here, we used the highly sensitive H atom Rydberg tagging time-of-flight method to conduct a crossed molecular beam scattering study of the F + H 2 → HF + H reaction with full quantum-state resolution. Pronounced forward-scattered HF products in the v ′ = 2 vibrational state were clearly observed at a collision energy of 0.52 kcal/mol; this was attributed to both the ground and the first excited Feshbach resonances trapped in the peculiar HF( v ′ = 3)-H′ vibrationally adiabatic potential, with substantial enhancement by constructive interference between the two resonances.