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

Published

November 1, 1999

Author(s)

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

Abstract

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 E_comm = 2.4 kcal/mole down to 0.3 kcal/mole. This energy range extends sugstantially below the theoretically predicted transition state barrier [E_barriernearly equal to} 1.9 kcal/mole; K. Stark and H. werner, J. Chem. Phys. 104, 6515 (1996) for the lowest adiabatic F(²P_3/2) + H₂ potential energy surface, therefore preferentially enhancing nonadiabatic channels due to spin-orbit excited F*(²P_1/2)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 (E_comnearly equal to} 0.3 kcal/mole), in contrast with exact adiabatic quantum calculations that predict a rapid decrease below E_com nearly equal to} 1.9 kcal/mole and vanishing reaction probability by E_comnearly equal to} 0.7 kcal/mol. Further evidence for a nonadiabatic F*(²P_1/2) 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(²P_3/2) 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.

Citation

Journal of Chemical Physics

Volume

111

Issue

No. 18

Pub Type

Journals

Keywords

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

Citation

Nizkorodov, S. , Harper, W. , Chapman, W. , Blackmon, B. and Nesbitt, D. (1999), Energy-Dependent Cross Sections and Nonadiabatic Reaction Dynamics in F(²P_3/2, ²P_1/2) + n-H₂ HF(v,J) + H, Journal of Chemical Physics (Accessed April 25, 2024)