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Science 24 August 2007:
Vol. 317. no. 5841, pp. 1061 - 1064
DOI: 10.1126/science.1144984
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Reports

Breakdown of the Born-Oppenheimer Approximation in the F + o-D2 -> DF + D Reaction

Li Che,1* Zefeng Ren,1* Xingan Wang,1 Wenrui Dong,1 Dongxu Dai,1 Xiuyan Wang,1 Dong H. Zhang,1 Xueming Yang,1{dagger} Liusi Sheng,2 Guoliang Li,3 Hans-Joachim Werner,3{dagger} François Lique,4 Millard H. Alexander4{dagger}

The reaction of F with H2 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(2P3/2) and excited F*(2P1/2) spin-orbit states with D2 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 reaction 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.

1 State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, People's Republic of (P. R.) China.
2 National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, P. R. China.
3 Institüt für Theoretische Chemie, Pfaffenwaldring 55, Universität Stuttgart, D-75069 Stuttgart, Germany.
4 Department of Chemistry and Biochemistry and Institute for Physical Sciences and Technology, University of Maryland, College Park, MD 20742–2021, USA.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: xmyang{at}dicp.ac.cn (X.Y.); werner{at}theochem.uni-stuttgart.de (H.-J.W.); mha{at}umd.edu (M.H.A.)

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