Reactive scattering of a supersonic fluorine atom beam: F + Cl₂

Abstract

Reactive scattering of F atoms with CI 2 molecules has been studied at an initial translational energy E ~ 32kJmo1-1, using a supersonic beam of F atoms seeded in He buffer gas. Laboratory angular and velocity distributions of FC1 product have been measured which show scattering peaking sharply in the forward direction with a smaller backward peak of relative height ~0'3 + 0.1. The product translational energy for scattering in the forward and backward directions is greater than that for the sideways scattering by a factor ~2. Reaction proceeds via a short-lived collision complex with a lifetime ~0-5 rotational periods for complexes rotating in the plane of collision. Bent structures are proposed for the collision complex and the reactant transition state, which relate the observed scattering to the initial orientation of the reactant CI 2 molecule with respect to the incident F atom direction.

Reactive scattering of a supersonic fluorine atom beam: F + Br2

“…The centre-of-mass angular distribution of figure 4 shows that the F + Br 2 reaction follows a direct stripping mechanism in contrast to the short-lived complex exhibited by the F + C12 reaction as described in the preceding paper [1]. The structure of the transition state in the entrance valley of the F + Br 2 potential energy surface may be estimated by reference to the structure proposed [1] for the F + C12 transition state.…”

“…The apparatus using mass spectrometric detection was the same as that employed in previous work [1] on the F + C12 reaction. The Br 2 beam issued from a monel nozzle with a diameter ~0.1 mm using a stagnation pressure~ 100Torr maintained by a Br 2 reservoir at a temperature ,-~ 10~…”

“…A molecular beam study of the reaction of fluorine atoms with chlorine molecules is reported in the preceding paper [1], in which the observed reaction dynamics are correlated with theoretical predictions of the topography of the F + C12 potential energy surface. It is of considerable interest to follow the variation in potential energy surface topography and the consequential nature of the reaction dynamics across the series of halogen atom-molecule exchange reactions, since this should yield general insight into the role of atomic electronegatives in determining chemical reaction dynamics [2].…”

“…Reactive scattering at high initial translational energies should be relatively insensitive to the long range potential between reactants and should therefore reflect the geometrical structure of the transition state more directly than studies at lower collision energy. This work presents reactive scattering measurements for the reaction of fluorine atoms with bromine molecules F+Br 2~FBr+Br (1) using a supersonic beam of F atoms seeded in He buffer gas. The rate constant for the F + Br 2 reaction has also been determined k = 1"9 x 1011 dm3mol -i s -1 at 298 K in a discharge flow experiment [5].…”

“…It is of considerable interest to follow the variation in potential energy surface topography and the consequential nature of the reaction dynamics across the series of halogen atom-molecule exchange reactions, since this should yield general insight into the role of atomic electronegatives in determining chemical reaction dynamics [2]. The reactions of chlorine atoms with bromine [3] and iodine [4] molecules have also been studied using supersonic beams of CI atoms seeded in inert buffer gases to give high initial translational energies E~25-75kJmo1- 1 and well defined kinematic resolution. Reactive scattering at high initial translational energies should be relatively insensitive to the long range potential between reactants and should therefore reflect the geometrical structure of the transition state more directly than studies at lower collision energy.…”