The reaction of chlorine atom Cl(2P) (Cl(2P3/2) and Cl* (2P1/2)) with D2 was investigated at collision energy from 4.5 kcal/mol to 6.5 kcal/mol with a high-resolution crossed molecular beam apparatus using the technique of D-atom Rydberg tagging detection.The contribution from the spin-orbit excited reaction Cl*(2P1/2)+D2,which is prohibited by BOppenheimer (BO) approximation,was observed.Collision-energy dependence of differential cross sections (DCSs) near the backward scattering direction was measured.The BO-forbidden reaction Cl*+D2 was found to be dominant at lower collision energy.As collision energy increases,reactivity of BO-allowed reaction Cl+D2 increases much faster than that of BO-forbidden reaction and becomes dominant at higher collision energy.Our experiment indicates that the additional energy of spin-orbit excitation in Cl* facilitates BO-forbidden reaction to pass through the barrier at lower collision energy,while BO approximation is still valid at collision energy near and above the reaction barrier.This tendency of reactivity of Cl/Cl*+D2 is similar to the isotopic reaction of Cl/Cl*+H2.