Displacement Dynamics of Fluorine Atoms Reacting with Bromobenzene and Iodobenzene Molecules

Abstract

Reactive scattering of F atoms with C 6 H 5 Br and C 6 H 5 I molecules leading to both hydrogen and halogen atom displacement has been studied at an initial translational energy E ∼ 38 kJ mol -1 using a supersonic beam of F atoms seeded in He buffer gas. The center-of-mass angular distributions of C 6 H 5 F reactive scattering show symmetrical forward and backward peaking, which is consistent with a long-lived collison complex, but the product translational energy distributions peak at a fraction f′ pk ∼ 0.18 of the total available energy and lie well above the predictions of phase space theory. The branching ratio ∼4 favors halogen atom over hydrogen atom displacement. The H atom displacement pathway is impeded by a potential energy barrier and occurs in competition with atom migration around the benzene ring. The halogen atom displacement occurs directly an F or H atom becomes bonded to the carbon atom adjacent to the halogen atom, following F atom or possibly H atom migration from other locations on the ring. The H atom displacement pathway for both FC 6 H 4 Br and FC 6 H 4 I reaction products shows a nominally isotropic angular distribution and a product translation energy distribution peaking at a fraction f′ pk ∼ 0.2 of the total available energy, in line with the H atom displacement dynamics previously observed for F + C 6 H 5 Cl.

Femtosecond Nucleophilic Substitution Reaction Dynamics

“…In this regard, our results support the theoretical studies of S N 2 reaction lifetimes (multiexponential), 5a,b consistent with nonconcerted S N 2 picture,5c and the experimental observation of vibrational excitation in products. 4a, Crossed beam studies of radical substitution reactions have been performed by the Lee and Grice groups 21b. We have also studied other systems, such as the reactions of Br - with IBz + and Cl - with p -iodotoluene cation, and obtained similar findings.…”

“…Consistent with the observations are the broad KETOF distributions which indicate vibrational energy involvement in some selective modes. In this regard, our results support the theoretical studies of S N 2 reaction lifetimes (multiexponential), 5a,b consistent with nonconcerted S N 2 picture,5c and the experimental observation of vibrational excitation in products. 4a, Crossed beam studies of radical substitution reactions have been performed by the Lee and Grice groups 21b.…”

Role of Renner Teller and Spin−Orbit Interaction in the Dynamics of the O(3P) + C3H5I Reaction

“…No evidence was found for the formation of HOI reaction product, as was observed 1,2 in the reactions of O( 3 P) atoms with C 2 H 5 I, (CH 3 ) 2 CHI, and (CH 3 ) 3 CI molecules. No reactive scattering which could be identified with the hypothetical displacement pathway was detected in these experiments.…”

“…Recent measurements of the reactive scattering of ground state O( 3 P) atoms with alkyl iodide molecules 1,2 have shown evidence for intersystem crossing from the initial triplet potential energy surface to the underlying singlet potential energy surface, resulting in the formation of both IO and HOI reaction products. [3][4][5] The IO product may be formed either by direct reaction over the triplet potential energy surface or by simple bond fission of the OIR singlet intermediate, while HOI product is formed by dissociation of the singlet OIR intermediate via a five-membered ring transition state.…”

Role of Renner Teller and Spin−Orbit Interaction in the Reactive Scattering of O(3P) Atoms with CF3I Molecules

“…Recent measurements , of the reactive scattering of O( 3 P) atoms with alkyl iodide molecules have demonstrated the role of intersystem crossing from the initial triplet potential energy surface to the underlying singlet potential energy surface which supports a stable OIR intermediate. This yields a long-lived collision complex which dissociates either by C−I bond fission to form IO product or via a five-membered ring transition state to form HOI product .…”