Energy Dependent Cross Sections and Nonadiabatic Reaction Dynamics in F(2P3/2, 2P1/2)+ n-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 exploited to investigate quantum state-resolved reactive scattering dynamics of F + n-H₂(j=0,1)->HF(v,J)+H in low density crossed supersomic jets under single collision conditions. Nascent rotational state distributions and relative cross sections for reactive scattering into the energetically highest (HF(v=3,J) vibrational manifold are obtained as a function of center-of-mass collision energies from E_com = 2.4 kcal/mole down to 0.3 kcal/mole. This energy range extends substantially below the theoretically predicted transition state barrier [E_barrier nearly equal to} 2.9 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 non-adiabatic channels due to spin orbit excited F^.2P_1/2) E_{spin orbit} = 1.15 kcal/mole) in the discharge source. The HF(v = 3, J) cross sections decrease gradually from 2.4 kcal/mole down to the lowest energies investigated (E_com nearly equal to}0.3 kcal/mole), in contrast with exact adiabatic quantum calculations which predict a rapid decrease below E_com nearly equal to}1.9 kcal/mole and vanishing reaction probability by E_com nearly equal to} 0.7 kcal/mol. Further evidence for non-adiabatic F^.(²P_1/2) reaction channel is provided by nascent rotational state distributions in HF(v=3, J), which are > 2-3 fold hotter than predicted by purely adiabatic calculations. Mostdramatically, the nascent product distributions reveal multiple HF(v=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 strong evidence for non-adiabatic dynamics involving multiple potential energy surfaces, even 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-HF(v,J)+H, Journal of Chemical Physics (Accessed March 14, 2025)