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Energy-Dependent Cross Sections and Nonadiabatic Reaction Dynamics in F(2P3/2, 2P1/2) + n-H2 HF(v,J) + H



S A. Nizkorodov, W W. Harper, W B. Chapman, B W. Blackmon, David Nesbitt


High-sensitivity direct IR laser absorption methods are expoited to investigate quantum state-resolved reactive scattering dynamics of F+n-H2(j=0,1)->HF(Ņ,J)+H in low-density crossed supersonic jets under single collision conditions. Nascent rotational state distributions and relative cross sections for reactive scattering into the energetically highest HF (Ņ=3,J) vibrational manifold are obtained as a function of center-of-mass collision energies from Ecomm = 2.4 kcal/mole down to 0.3 kcal/mole. This energy range extends sugstantially below the theoretically predicted transition state barrier [Ebarriernearly equal to} 1.9 kcal/mole; K. Stark and H. werner, J. Chem. Phys. 104, 6515 (1996) for the lowest adiabatic F(2P3/2) + H2 potential energy surface, therefore preferentially enhancing nonadiabatic channels due to spin-orbit excited F*(2P1/2)δ E spin-orbit = 1.15 kcal/mole) in the discharge source. The HF (Ņ=3,J) cross sections decrease gradually from 2.4 kcal/mole down to the lowest energies investigated (Ecomnearly equal to} 0.3 kcal/mole), in contrast with exact adiabatic quantum calculations that predict a rapid decrease below Ecom nearly equal to} 1.9 kcal/mole and vanishing reaction probability by Ecomnearly equal to} 0.7 kcal/mol. Further evidence for a nonadiabatic F*(2P1/2) reaction channel is provided by nascent rotational state distribitions in HF (Ņ=3,J), which are > 2-3 fold hotter than predicted by purely adiabatic calculations. Most dramatically, the nascent product distributions reveal multiple HF (Ņ=3,J) rovibrational states that would be energetically inaccessible from ground state F(2P3/2) atom reactions. These quantum state resolved reactive scattering studies provide the first evidence for finite nonadiabatic dynamics involving multiple potential energy surfaces in this well-studied benchmark F+H2 reaction system.
Journal of Chemical Physics
No. 18


absorption crossed jets, fluorine, hydrogen, non-adiabatic effects, reaction dynamics


Nizkorodov, S. , Harper, W. , Chapman, W. , Blackmon, B. and Nesbitt, D. (1999), Energy-Dependent Cross Sections and Nonadiabatic Reaction Dynamics in F(<sup>2</sup>P<sub>3/2</sub>, <sup>2</sup>P<sub>1/2</sub>) + n-H<sub>2</sub> HF(v,J) + H, Journal of Chemical Physics (Accessed December 11, 2023)
Created October 31, 1999, Updated October 12, 2021