Breakdown of the Born-Oppenheimer Approximation in the F+ o -D 2 → DF + D Reaction

• DOI: 10.1126/science.1144984
• Publication Date: 2007-08-23T20:53:54Z
• Authors: Li Che; Zefeng Ren; Xingan Wang; Wenrui Dong; Dongxu Dai; Xiuyan Wang; Dong H. Zhang; Xueming Yang; Liusi Sheng; Guoliang Li; Hans-Joachim Werner; François Lique; Millard H. Alexander
• Keywords: Isotopomers; Crossed molecular beam; Born–Oppenheimer approximation; Exothermic reaction; Born approximation; Triatomic molecule; Reactivity; Kinetic isotope effect

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 differential cross sections ground F( P 3/2 ) excited F*( 1/2 spin-orbit states D collision energies 0.25 to 1.2 kilocalorie/mole. At lowest energy, F* ∼1.6 times more reactive than F, although forbidden within Born-Oppenheimer (BO) approximation. As energy increases, BO-allowed rapidly dominates. We found excellent agreement between multistate, quantum calculations both measured dependence F*/F reactivity ratio sections. This confirms fundamental understanding factors controlling electronic nonadiabaticity in reactions.