This thesis addresses two important and also challenging issues in the research of chemical reaction dynamics of F+H2 system. One is to probe the reaction resonance and the other is to determine the extent of the breakdown of the Born-Oppenheimer approximation (BOA) experimentally. The author introduces a state-of-the-art crossed molecular beam-scattering apparatus using a hydrogen atom Rydberg "tagging" time-of-flight method, and presents thorough state-to-state experimental studies to address the above issues. The author also describes the observation of the Feshbach resonance in the...