Breakdown of the Born-Oppenheimer Approximation in the F + o-D_2 →DF + D Reaction

摘要

The reaction of F with H_2 and its isotopomers is the paradigm for an exothermic triatomic abstraction reaction. In a crossed-beam scattering experiment, we determined relative integral and differential cross sections for reaction of the ground F(~2P_(3/2) and excited F~*(~2P_(-/2) spin-orbit states with D_2 for collision energies of 0.25 to 1.2 kilocalorie/mole. At the lowest collision energy, F~* is ～1.6 times more reactive than F, although reaction of F~* is forbidden within the Born-Oppenheimer (BO) approximation. As the collision energy increases, the BO-allowed reactior rapidly dominates. We found excellent agreement between multistate, quantum reactive scattering calculations and both the measured energy dependence of the F~*/F reactivity ratio and the differential cross sections. This agreement confirms the fundamental understanding of the factors controlling electronic nonadiabaticity in abstraction reactions.